
The (; ) were introduced as non-citizen troops attached to the citizen
legions by
Augustus
Gaius Julius Caesar Augustus (born Gaius Octavius; 23 September 63 BC – 19 August AD 14), also known as Octavian (), was the founder of the Roman Empire, who reigned as the first Roman emperor from 27 BC until his death in A ...
after his reorganisation of the
Imperial Roman army from 27 BC. By the 2nd century, the contained the same number of infantry as the legions and, in addition, provided almost all of the Roman army's
cavalry
Historically, cavalry (from the French word ''cavalerie'', itself derived from ''cheval'' meaning "horse") are groups of soldiers or warriors who Horses in warfare, fight mounted on horseback. Until the 20th century, cavalry were the most mob ...
(especially
light cavalry
Light cavalry comprised lightly armed and body armor, armored cavalry troops mounted on fast horses, as opposed to heavy cavalry, where the mounted riders (and sometimes the warhorses) were heavily armored. The purpose of light cavalry was p ...
and
archers) and more specialised troops. The thus represented three-fifths of Rome's regular land forces at that time. Like their legionary counterparts, auxiliary recruits were mostly volunteers, not conscripts.
The were mainly recruited from the ''
peregrini'', free provincial subjects who did not hold
Roman citizenship
Citizenship in ancient Rome () was a privileged political and legal status afforded to free individuals with respect to laws, property, and governance. Citizenship in ancient Rome was complex and based upon many different laws, traditions, and cu ...
and constituted the vast majority of the population in the 1st and 2nd centuries (c. 90% in the early 1st century). In contrast to the legions, which only admitted
Roman citizens, members of the could be recruited from territories outside of Roman control.
Reliance on the various contingents of non-
Italic troops, especially cavalry, increased when the
Roman Republic
The Roman Republic ( ) was the era of Ancient Rome, classical Roman civilisation beginning with Overthrow of the Roman monarchy, the overthrow of the Roman Kingdom (traditionally dated to 509 BC) and ending in 27 BC with the establis ...
employed them in increasing numbers to support its legions after 200 BC. The
Julio-Claudian period (27 BC–68 AD) saw the transformation of the from motley
levies to a standing corps with standardised structure, equipment and conditions of service. By the end of the period, there were no significant differences between legionaries and auxiliaries in terms of training and combat capability.
Auxiliary regiments were often stationed in provinces other than that in which they were originally raised, for reasons of security and to foster the process of
Romanization
In linguistics, romanization is the conversion of text from a different writing system to the Latin script, Roman (Latin) script, or a system for doing so. Methods of romanization include transliteration, for representing written text, and tra ...
in the provinces. The regimental names of many auxiliary units persisted into the 4th century, but by then the units in question were different in size, structure, and quality from their predecessors.
Historical development
Background: Roman Republic (to 30 BC)
The mainstay of the Roman republic's war machine was the
manipular legion, a
heavy infantry unit suitable for close-quarter engagements on more or less any terrain, which was probably adopted sometime during the
Samnite Wars
The First, Second, and Third Samnite Wars (343–341 BC, 326–304 BC, and 298–290 BC) were fought between the Roman Republic and the Samnites, who lived on a stretch of the Apennine Mountains south of Rome and north of the Lucanian tribe.
...
(343–290 BC). Despite its formidable strength, the legion had a number of deficiencies, especially a lack of cavalry. Around 200 BC, a legion of 4,200 infantry had a cavalry arm of only 300 horse (just 7% of the total force). This was because the class of citizens who could afford to pay for their own horse and equipment – the
equestrian order
The (; , though sometimes referred to as " knights" in English) constituted the second of the property/social-based classes of ancient Rome, ranking below the senatorial class. A member of the equestrian order was known as an ().
Descript ...
, the second rank in Roman society, after the
senatorial order – was relatively small. In addition, the legion lacked missile forces such as slingers and archers. Until 200 BC, the bulk of a Roman army's cavalry was provided by Rome's regular Italian allies (''
socii
The ''socii'' ( ) or ''foederati'' ( ) were confederates of ancient Rome, Rome and formed one of the three legal denominations in Roman Italy (''Italia'') along with the core Roman citizens (''Cives Romani'') and the extended ''Latin Rights, Lat ...
''), commonly known as the "Latin" allies, which made up the
Roman military confederation. This was Rome's defence system until the
Social War of 91–88 BC. The Italian forces were organised into ''
alae'' (literally 'wings', because they were generally posted on the flanks of the Roman line of battle). An allied , commanded by three Roman , was similar or slightly larger in infantry size (4–5,000 men) to a legion, but contained a more substantial cavalry contingent: 900 horse, three times the legionary contingent. Since a pre-Social War
consular army always contained an equal number of legions and , 75% of its cavalry was provided by the Latin allies. The overall cavalry element, c. 12% of the total force (2,400 out of a normal consular army of approximately 20,000 total effectives), was greater than in most peninsular Italian forces, but well below the overall 21% cavalry component that was typical of the
Principate
The Principate was the form of imperial government of the Roman Empire from the beginning of the reign of Augustus in 27 BC to the end of the Crisis of the Third Century in AD 284, after which it evolved into the Dominate. The principate was ch ...
army (80,000 cavalry out of 380,000 total effectives in the early 2nd century).
[Holder (2003) 145][Hassall (2000) 320]
The Roman/Latin cavalry was sufficient while Rome was in conflict with other states in the mountainous Italian peninsula, which also disposed of limited cavalry resources. But, as Rome was confronted by external enemies that deployed far more powerful cavalry elements, such as the
Gauls
The Gauls (; , ''Galátai'') were a group of Celts, Celtic peoples of mainland Europe in the Iron Age Europe, Iron Age and the Roman Gaul, Roman period (roughly 5th century BC to 5th century AD). Their homeland was known as Gaul (''Gallia''). Th ...
and the
Carthaginians
The Punic people, usually known as the Carthaginians (and sometimes as Western Phoenicians), were a Semitic people, Semitic people who Phoenician settlement of North Africa, migrated from Phoenicia to the Western Mediterranean during the Iron ...
, the Roman deficiency in cavalry numbers could be a serious liability, which in the
Second Punic War
The Second Punic War (218 to 201 BC) was the second of Punic Wars, three wars fought between Ancient Carthage, Carthage and Roman Republic, Rome, the two main powers of the western Mediterranean Basin, Mediterranean in the 3rd century BC. For ...
(218–202 BC) resulted in crushing defeats.
Hannibal
Hannibal (; ; 247 – between 183 and 181 BC) was a Punic people, Carthaginian general and statesman who commanded the forces of Ancient Carthage, Carthage in their battle against the Roman Republic during the Second Punic War.
Hannibal's fat ...
's major victories at the
Trebia and at
Cannae, were owed to his Spanish and Gallic heavy cavalry, which far outnumbered the Roman and Latin levies, and to his
Numidia
Numidia was the ancient kingdom of the Numidians in northwest Africa, initially comprising the territory that now makes up Algeria, but later expanding across what is today known as Tunisia and Libya. The polity was originally divided between ...
ns, light, fast cavalry which the Romans wholly lacked. The decisive Roman victory at
Zama in 202 BC, which ended the war, owed much to the
Numidian cavalry
Numidian cavalry was a type of light cavalry developed by the Numidians. They were used by Hannibal during the Punic Wars, and later became commonplace in the Roman army of the late Republic.
History
Numidian cavalry is first mentioned by Polybi ...
provided by king
Massinissa, which outnumbered the Roman/Latin cavalry fielded by two to one. From then, Roman armies were always accompanied by large numbers of non-Italian cavalry: Numidian light cavalry and, later, Gallic heavy cavalry. For example, Caesar relied heavily on Gallic and German cavalry for his
Conquest of Gaul
The Gallic Wars were waged between 58 and 50 BC by the Roman general Julius Caesar against the peoples of Gaul (present-day France, Belgium, and Switzerland). Gallic, Germanic, and Brittonic tribes fought to defend their homelands ag ...
(58–51 BC).
[Goldsworthy (2000) 126]
As the role of native cavalry grew, that of Roman/Latin cavalry diminished. In the early 1st century BC, Roman cavalry was phased out altogether. After the Social War, the were all granted Roman citizenship, the Latin ' abolished, and the ' recruited into the legions. Furthermore, Roman equestrians were no longer required to perform cavalry service after this time. The late Republican legion was thus probably bereft of cavalry (a tiny cavalry force of 120 men was probably added back to the legion under
Augustus
Gaius Julius Caesar Augustus (born Gaius Octavius; 23 September 63 BC – 19 August AD 14), also known as Octavian (), was the founder of the Roman Empire, who reigned as the first Roman emperor from 27 BC until his death in A ...
).
By the outbreak of the Second Punic War, the Romans were remedying the legions' other deficiencies by using non-Italian specialised troops. Livy reports
Hiero of
Syracuse offering to supply Rome with archers and slingers in 217 BC. From 200 BC onwards, specialist troops were hired as
mercenaries on a regular basis: (archers) from
Crete
Crete ( ; , Modern Greek, Modern: , Ancient Greek, Ancient: ) is the largest and most populous of the Greek islands, the List of islands by area, 88th largest island in the world and the List of islands in the Mediterranean#By area, fifth la ...
, and (
slingers) from the
Balearic Isles almost always accompanied Roman legions in campaigns all over the Mediterranean.
The other main sources of non-Italian troops in the late Republic were subject provincials, allied cities and Rome's (satellite kings). During the late Republic, non-Italian units were led by their own native chiefs, and their internal organisation was left to their own commanders. The units varied widely in dress, equipment, and weapons. They were normally raised for specific campaigns and often disbanded soon afterwards, in a similar manner to the earlier ' militia legions.
Foundation of the auxilia under Augustus (30 BC–14 AD)
It appears that not all indigenous units were disbanded at the end of the civil war period (31 BC). Some of the more experienced units were kept in existence to complement the legions, and became the core of the standing auxiliary forces that developed in the
Julio-Claudian period. During the early part of Augustus' rule (27 BC onwards), the corps of regular Auxilia was created. It was clearly inspired by the Latin forces of the pre-Social War Republic, as a corps of non-citizen troops parallel to the legions. But there were fundamental differences, the same as between Republican and Augustan legions. The Latin forces of the Republic were made up of part-time conscripts in units that would be raised and disbanded for and after particular campaigns. The Augustan Auxilia were mainly volunteer professionals serving in permanent units.
The unit structure of the Auxilia also differed from the Latin ', which were like legions with a larger cavalry arm. However, Augustus organised the Auxilia into regiments the size of
cohorts (a tenth the size of legions), due to the much greater flexibility of the smaller unit size. Further, the regiments were of three types: ''
ala'' (cavalry), ''
cohors (peditata)'' (infantry) and ''
cohors equitata'' (mixed cavalry/infantry).
[Goldsworthy (2000) 127]
The evidence for the size of the Augustus' new units is not clear-cut, with our most precise evidence dating to the 2nd century, by which time the unit strengths may have changed. were likely modelled on legionary cohorts i.e. six of about 80 men each (total about 480 men). ' were divided into (squadrons) of 30 (or 32) men, each under a (literally: 'leader of ten'). This title derives from the old Roman cavalry of the pre-Social War republic, in which each was under the command of three . were infantry with a cavalry contingent of four attached.
Auxiliary regiments were now led by a (prefect), who could be either a native nobleman, who would probably be granted Roman citizenship for the purpose (e.g. the famous German war leader
Arminius
Arminius (; 18/17 BC–AD 21) was a chieftain of the Germanic peoples, Germanic Cherusci tribe who is best known for commanding an alliance of Germanic tribes at the Battle of the Teutoburg Forest in AD 9, in which three Roman legions under th ...
gained Roman citizenship probably by serving as an auxiliary prefect before turning against Rome); or a Roman, either of
knightly rank, or a senior
centurion.
At the start of Augustus' sole rule (30 BC), the original core auxiliary units in the West were composed of warlike tribesmen from the Gallic provinces (especially
Gallia Belgica, which then included the regions later separated to form the provinces
Germania Inferior
''Germania Inferior'' ("Lower Germania") was a Roman province from AD 85 until the province was renamed ''Germania Secunda'' in the 4th century AD, on the west bank of the Rhine bordering the North Sea. The capital of the province was Colonia Cl ...
and
Germania Superior
Germania Superior ("Upper Germania") was an imperial province of the Roman Empire. It comprised an area of today's western Switzerland, the French Jura and Alsace regions, and southwestern Germany. Important cities were Besançon ('' Vesont ...
), and from the Balkan provinces (
Dalmatia
Dalmatia (; ; ) is a historical region located in modern-day Croatia and Montenegro, on the eastern shore of the Adriatic Sea. Through time it formed part of several historical states, most notably the Roman Empire, the Kingdom of Croatia (925 ...
and
Illyricum). By 19 BC, the
Cantabrian and Asturian Wars were concluded, leading to the annexation of northern
Hispania
Hispania was the Ancient Rome, Roman name for the Iberian Peninsula. Under the Roman Republic, Hispania was divided into two Roman province, provinces: Hispania Citerior and Hispania Ulterior. During the Principate, Hispania Ulterior was divide ...
and
Lusitania
Lusitania (; ) was an ancient Iberian Roman province encompassing most of modern-day Portugal (south of the Douro River) and a large portion of western Spain (the present Extremadura and Province of Salamanca). Romans named the region after th ...
. Judging by the names of attested auxiliary regiments, these parts of the Iberian peninsula soon became a major source of recruits. Then the Danubian regions were annexed:
Raetia (annexed 15 BC),
Noricum
Noricum () is the Latin name for the kingdom or federation of tribes that included most of modern Austria and part of Slovenia. In the first century AD, it became a province of the Roman Empire. Its borders were the Danube to the north, R ...
(16 BC),
Pannonia
Pannonia (, ) was a Roman province, province of the Roman Empire bounded on the north and east by the Danube, on the west by Noricum and upper Roman Italy, Italy, and on the southward by Dalmatia (Roman province), Dalmatia and upper Moesia. It ...
(9 BC) and
Moesia
Moesia (; Latin: ''Moesia''; ) was an ancient region and later Roman province situated in the Balkans south of the Danube River. As a Roman domain Moesia was administered at first by the governor of Noricum as 'Civitates of Moesia and Triballi ...
(6 AD), becoming, with Illyricum, the Principate's most important source of auxiliary recruits for its entire duration. In the East, where the Syrians already provided the bulk of the Roman army's archers, Augustus annexed
Galatia (25 BC) and
Judaea: the former, a region in central Anatolia with a Celtic-speaking people, became an important source of recruits. In N. Africa, Egypt,
Cyrene, and
Numidia
Numidia was the ancient kingdom of the Numidians in northwest Africa, initially comprising the territory that now makes up Algeria, but later expanding across what is today known as Tunisia and Libya. The polity was originally divided between ...
(25 BC) were added to the empire. Numidia (modern day Eastern Algeria) was home to the Numidians/Moors, the ancestors of today's
Berber people. Their light cavalry (''equites Maurorum'') was highly prized and had alternately fought and assisted the Romans for well over two centuries: they now started to be recruited into the regular Auxilia. Even more Mauri units were formed after the annexation of
Mauretania
Mauretania (; ) is the Latin name for a region in the ancient Maghreb. It extended from central present-day Algeria to the Atlantic Ocean, Atlantic, encompassing northern present-day Morocco, and from the Mediterranean Sea, Mediterranean in the ...
(NW Algeria, Morocco), the rest of the Berber homeland, in 44 AD by emperor
Claudius
Tiberius Claudius Caesar Augustus Germanicus ( ; ; 1 August 10 BC – 13 October AD 54), or Claudius, was a Roman emperor, ruling from AD 41 to 54. A member of the Julio-Claudian dynasty, Claudius was born to Nero Claudius Drusus, Drusus and Ant ...
(ruled 41–54).
Recruitment was thus heavy throughout the Augustan period, with a steady increase in the number of units formed. By AD 23, the Roman historian
Tacitus
Publius Cornelius Tacitus, known simply as Tacitus ( , ; – ), was a Roman historian and politician. Tacitus is widely regarded as one of the greatest Roman historians by modern scholars.
Tacitus’ two major historical works, ''Annals'' ( ...
records that there were roughly the same numbers of auxiliaries in service as there were legionaries. Since at this time there were 25 legions of c. 5,000 men each, the Auxilia thus amounted to c. 125,000 men, implying c. 250 auxiliary regiments.
Illyrian revolt (6–9 AD)
During the early Julio-Claudian period, many auxiliary regiments raised in frontier provinces were stationed in or near their home provinces, except during periods of major crises such as the
Cantabrian Wars, when they were deployed temporarily in theatre. This carried the obvious risk if their own tribe or ethnic group rebelled against Rome (or attacked the Roman frontier from outside the Empire), auxiliary troops could be tempted to make common cause with them. The Romans would then be faced by an enemy that included units fully equipped and trained by themselves, thus losing their usual tactical advantages over tribal foes.
[Keppie (1996) 396]
The German leader
Arminius
Arminius (; 18/17 BC–AD 21) was a chieftain of the Germanic peoples, Germanic Cherusci tribe who is best known for commanding an alliance of Germanic tribes at the Battle of the Teutoburg Forest in AD 9, in which three Roman legions under th ...
is the classic example at an individual level: after several years of serving in Rome's forces as prefect of an auxiliary unit, he used the military training and experience he had gained to lead a confederacy of German tribes against Rome, culminating in the destruction of three Roman legions in the
Teutoberg Forest in 9 AD, and the abandonment of Augustus' strategy of annexing Germany as far as the
Elbe
The Elbe ( ; ; or ''Elv''; Upper Sorbian, Upper and , ) is one of the major rivers of Central Europe. It rises in the Giant Mountains of the northern Czech Republic before traversing much of Bohemia (western half of the Czech Republic), then Ge ...
river. (This strategy was never revived by later emperors).
At a collective level, the risk was even greater, as the hugely dangerous
Illyrian revolt proved. The central Illyrian tribes were tough and spartan shepherds of the
Bosnian mountains and excellent soldier material. Their territory formed part of the strategic province of Illyricum, recently expanded to include the territory of the
Pannonii, Celticised Illyrian tribes based on the west bank of the
Danube
The Danube ( ; see also #Names and etymology, other names) is the List of rivers of Europe#Longest rivers, second-longest river in Europe, after the Volga in Russia. It flows through Central and Southeastern Europe, from the Black Forest sou ...
who were subjugated by Rome in 12–9 BC (the ). By the start of the Common Era, they were an important recruitment base for the auxilia. But discontent was festering among the Illyrian tribes, largely due to what they saw as the rapacity of Roman tax officials. In AD 6, several regiments of
Dalmatae, a warlike Illyrian tribe, were ordered to report to a designated location to prepare to join Augustus' stepson and senior military commander
Tiberius
Tiberius Julius Caesar Augustus ( ; 16 November 42 BC – 16 March AD 37) was Roman emperor from AD 14 until 37. He succeeded his stepfather Augustus, the first Roman emperor. Tiberius was born in Rome in 42 BC to Roman politician Tiberius Cl ...
in a war against the Germans. Instead, they mutinied at the assembly point, and defeated a Roman force sent against them. The Dalmatae were soon joined by the
Breuci, another Illyrian tribe that supplied several auxiliary regiments. They gave battle to a second Roman force from
Moesia
Moesia (; Latin: ''Moesia''; ) was an ancient region and later Roman province situated in the Balkans south of the Danube River. As a Roman domain Moesia was administered at first by the governor of Noricum as 'Civitates of Moesia and Triballi ...
. They lost, but inflicted heavy casualties. The rebels were now joined by a large number of other Illyrian tribes. The Dalmatae attacked the port of
Salona and overran the Adriatic coast, defeating a Roman force and exposing the Roman heartland of Italy to the fear of a rebel invasion.
Augustus ordered Tiberius to break off operations in Germany and move his main army to Illyricum. When it became clear that even Tiberius' forces were insufficient, Augustus was obliged to raise a second task force under Tiberius' nephew
Germanicus
Germanicus Julius Caesar (24 May 15 BC – 10 October AD 19) was a Roman people, Roman general and politician most famously known for his campaigns against Arminius in Germania. The son of Nero Claudius Drusus and Antonia the Younger, Germanicu ...
, resorting to the compulsory purchase and emancipation of thousands of slaves to find enough troops, for the first time since the aftermath of the Battle of Cannae over two centuries earlier. The Romans had now deployed no less than 15 legions and an equivalent number of auxilia.
[Suetonius III.16] This amounts to a total of c. 150,000 men, including at least 50 auxiliary cohorts composed, exceptionally, of Roman citizens. These were men whose status or background was regarded by Augustus as unsuitable for recruitment into the legions: either natural-born citizens of the lowest category, including vagrants and convicted criminals, or the freed slaves (Roman law accorded citizenship to the freed slaves of Roman citizens). These special units were accorded the title ('of Roman citizens'), or ''c.R.'' for short. After the Illyrian revolt, these cohorts remained in being and recruited non-citizens like other auxiliary units, but retained their prestigious ''c.R.'' title.
In addition, the regular forces were assisted by a large number of allied troops from neighbouring
Thrace
Thrace (, ; ; ; ) is a geographical and historical region in Southeast Europe roughly corresponding to the province of Thrace in the Roman Empire. Bounded by the Balkan Mountains to the north, the Aegean Sea to the south, and the Black Se ...
deployed by their king
Rhoemetalces I, a Roman (puppet king).
The Romans faced further reverses on the battlefield and a savage guerrilla war in the Bosnian mountains. It took them three years of hard fighting to quell the revolt, which was described by the Roman historian
Suetonius
Gaius Suetonius Tranquillus (), commonly referred to as Suetonius ( ; – after AD 122), was a Roman historian who wrote during the early Imperial era of the Roman Empire. His most important surviving work is ''De vita Caesarum'', common ...
, writing in c. AD 100, as the most difficult conflict faced by Rome since the
Punic Wars
The Punic Wars were a series of wars fought between the Roman Republic and the Ancient Carthage, Carthaginian Empire during the period 264 to 146BC. Three such wars took place, involving a total of forty-three years of warfare on both land and ...
over two centuries earlier.
Tiberius finally succeeded in quelling the revolt in 9 AD. This was apparently lucky timing for the Romans: that same year Arminius destroyed
Varus' three legions in Germany. The Roman high command had no doubt that Arminius would have formed a grand alliance with the Illyrians.
Despite the gravity of this rebellion, the Illyrians went on, alongside their neighbours the Thracians, to become the backbone of the Roman army. By the 2nd century, with roughly half the Roman army deployed on the Danube frontier, the auxilia and legions alike were dominated by Illyrian recruits. In the 3rd century, Illyrians largely replaced Italians in the senior officer echelons of of auxiliary regiments and of legions. Finally, from AD 268 to 379, virtually all emperors, including
Diocletian
Diocletian ( ; ; ; 242/245 – 311/312), nicknamed Jovius, was Roman emperor from 284 until his abdication in 305. He was born Diocles to a family of low status in the Roman province of Dalmatia (Roman province), Dalmatia. As with other Illyri ...
and
Constantine the Great
Constantine I (27 February 27222 May 337), also known as Constantine the Great, was a Roman emperor from AD 306 to 337 and the first Roman emperor to convert to Christianity. He played a Constantine the Great and Christianity, pivotal ro ...
, were Romanised Illyrians from the provinces of
Dalmatia
Dalmatia (; ; ) is a historical region located in modern-day Croatia and Montenegro, on the eastern shore of the Adriatic Sea. Through time it formed part of several historical states, most notably the Roman Empire, the Kingdom of Croatia (925 ...
,
Moesia Superior and
Pannonia
Pannonia (, ) was a Roman province, province of the Roman Empire bounded on the north and east by the Danube, on the west by Noricum and upper Roman Italy, Italy, and on the southward by Dalmatia (Roman province), Dalmatia and upper Moesia. It ...
. These were members of a military aristocracy, outstanding soldiers who saved the empire from collapse in the turbulent late 3rd century.
Later Julio-Claudians (14–68 AD)

Significant development of the Auxilia appears to have taken place during the rule of the emperor
Claudius
Tiberius Claudius Caesar Augustus Germanicus ( ; ; 1 August 10 BC – 13 October AD 54), or Claudius, was a Roman emperor, ruling from AD 41 to 54. A member of the Julio-Claudian dynasty, Claudius was born to Nero Claudius Drusus, Drusus and Ant ...
(41–54 AD).
A minimum term of service of 25 years was established, at the end of which the retiring auxiliary soldier, and all his children, were awarded Roman citizenship.
[Keppie (1996) 391] This is deduced from the fact that the first known
Roman military diplomas date from the time of Claudius. This was a folding bronze tablet engraved with the details of the soldier's service record, which he could use to prove his citizenship. Claudius also decreed that prefects of auxiliary regiments must all be of equestrian rank, thus excluding centurions from such commands.
The fact that auxiliary commanders were now all of the same social rank as most ''
tribuni militum'', (military tribunes, a legion's senior staff officers, all of whom only one, the , was of the higher senatorial rank), probably indicates that auxilia now enjoyed greater prestige. Indigenous chiefs continued to command some auxiliary regiments, and were probably granted equestrian rank for the purpose. It is also likely that auxiliary pay was standardised at this time, but we only have estimates for the Julio-Claudian period.
Auxiliary uniform, armour, weapons and equipment were probably standardised by the end of the Julio-Claudian period. Auxiliary equipment was broadly similar to that of the legions (see
Section 2.1 below for possible differences in armour). By 68 AD, there was little difference between most auxiliary infantry and their legionary counterparts in equipment, training and fighting capability. The main difference was that auxilia contained combat cavalry, both heavy and light, and other specialized units that legions lacked.
Claudius annexed to the empire three regions that became important sources of auxiliary recruits:
Britannia
The image of Britannia () is the national personification of United Kingdom, Britain as a helmeted female warrior holding a trident and shield. An image first used by the Romans in classical antiquity, the Latin was the name variously appli ...
(43 AD), and the former client kingdoms of
Mauretania
Mauretania (; ) is the Latin name for a region in the ancient Maghreb. It extended from central present-day Algeria to the Atlantic Ocean, Atlantic, encompassing northern present-day Morocco, and from the Mediterranean Sea, Mediterranean in the ...
(44) and
Thracia
Thracia or Thrace () is the ancient name given to the southeastern Balkans, Balkan region, the land inhabited by the Thracians. Thrace was ruled by the Odrysian kingdom during the Classical Greece, Classical and Hellenistic period, Hellenis ...
(46). The latter became as important as Illyria as a source of auxiliary recruits, especially cavalry and archers. Britain in mid-2nd century contained the largest number of auxiliary regiments in any single province: about 60 out of about 400 (15%).
By the rule of
Nero
Nero Claudius Caesar Augustus Germanicus ( ; born Lucius Domitius Ahenobarbus; 15 December AD 37 – 9 June AD 68) was a Roman emperor and the final emperor of the Julio-Claudian dynasty, reigning from AD 54 until his ...
(54–68), auxiliary numbers may have reached, by one estimate, about 200,000 men, implying about 400 regiments.
Revolt of the Batavi (69–70 AD)

The
Batavi, a Germanic tribe, inhabited the region today known as
Gelderland
Gelderland ( , ), also known as Guelders ( ) in English, is a Provinces of the Netherlands, province of the Netherlands, located in the centre-east of the country. With a total area of of which is water, it is the largest province of the Nethe ...
(
Netherlands
, Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...
), in the Rhine river
delta
Delta commonly refers to:
* Delta (letter) (Δ or δ), the fourth letter of the Greek alphabet
* D (NATO phonetic alphabet: "Delta"), the fourth letter in the Latin alphabet
* River delta, at a river mouth
* Delta Air Lines, a major US carrier ...
, then known as the ('Island of the Batavi', because it is surrounded by branches of the Rhine), part of the Roman province of
Germania Inferior
''Germania Inferior'' ("Lower Germania") was a Roman province from AD 85 until the province was renamed ''Germania Secunda'' in the 4th century AD, on the west bank of the Rhine bordering the North Sea. The capital of the province was Colonia Cl ...
.
[Tacitus ''Historiae'' IV.18] They were a warlike people, skilled horsemen, boatmen and swimmers. In return for the unusual privilege of exemption from (direct taxes on land and heads normally exacted from ), they supplied a disproportionate number of recruits to the Julio-Claudian auxilia: one ' and eight . They also provided most of Augustus' elite personal bodyguard unit (the ), which continued in service until 68 AD. The Batavi auxilia amounted to about 5,000 men, implying that during the entire Julio-Claudian period, over 50% of all Batavi males reaching military age (16 years) may have enlisted in the auxilia.
[Birley (2002) 43] Thus the Batavi, although just 0.05% of the total population of the empire of c. 70 million in 23 AD, supplied about 4% of the total auxilia i.e. 80 times their proportionate share. They were regarded by the Romans as the very best (, ) of their auxiliary, and indeed all, their forces. In Roman service, both their cavalry and infantry had perfected a technique for swimming across rivers wearing full armour and weapons.
Julius Civilis (, clearly a Latin name adopted on gaining
Roman citizenship
Citizenship in ancient Rome () was a privileged political and legal status afforded to free individuals with respect to laws, property, and governance. Citizenship in ancient Rome was complex and based upon many different laws, traditions, and cu ...
, not his native one) was a hereditary prince of the Batavi and the prefect of a Batavi cohort. A veteran of 25 years' service, he had distinguished himself by service in Britain, where he and the eight Batavi cohorts had played a crucial role in both the
Roman invasion in 43 AD and the subsequent subjugation of southern Britain.
By 69, however, Civilis, the Batavi regiments and the Batavi people had become utterly disaffected with Rome. After the Batavi regiments were withdrawn from Britain to Italy in 66, Civilis and his brother (also a prefect) were arrested by the
governor of Germania Inferior on a fabricated accusation of sedition. The governor ordered his brother's execution, while Civilis, who as a Roman citizen had the right to appeal to the emperor, was sent to Rome in chains for judgement by Nero. He was released by Nero's overthrower and successor,
Galba, but the latter also disbanded the imperial bodyguard unit for their loyalty to Nero. This alienated several hundred crack Batavi troops, and indeed the whole Batavi nation who regarded it as a grave insult. At the same time, relations collapsed between the Batavi cohorts and the legion to which they had been attached since the invasion of Britain 25 years earlier (''
XIV Gemina''). Their mutual hatred erupted in open fighting on at least two occasions.
At this juncture, the Roman empire was convulsed by its first major civil war since the
Battle of Actium exactly a century earlier: the
Year of the Four Emperors (69–70 AD). The governor of Germania Inferior, ordered to raise more troops, outraged the Batavi by attempting to conscript more Batavi than the maximum stipulated in their treaty. The brutality and corruption of the Roman recruiting-centurions (including incidents of sexual assault on Batavi young men) brought already deep discontent in the Batavi homeland to the boil.
Civilis now led his people in open revolt. Initially, he claimed he was supporting the bid for power of
Vespasian
Vespasian (; ; 17 November AD 9 – 23 June 79) was Roman emperor from 69 to 79. The last emperor to reign in the Year of the Four Emperors, he founded the Flavian dynasty, which ruled the Empire for 27 years. His fiscal reforms and consolida ...
, the general in command of the legions in
Syria
Syria, officially the Syrian Arab Republic, is a country in West Asia located in the Eastern Mediterranean and the Levant. It borders the Mediterranean Sea to the west, Turkey to Syria–Turkey border, the north, Iraq to Iraq–Syria border, t ...
, whom Civilis had probably befriended when both were involved in the Roman invasion of Britain 25 years earlier (Vespasian was then commander of the legion ''
II Augusta''). But the uprising soon became a bid for independence. Civilis exploited the fact that some legions were absent from the Rhine area due to the civil war, and the rest under-strength. In addition, the Roman commanders and their rank-and-file soldiers were divided by loyalty to rival emperors. Civilis quickly won the support of the Batavi's neighbours and kinsmen, the
Cananefates, who in turn won over the
Frisii
The Frisii were an ancient tribe, who were neighbours of the Roman empire in the low-lying coastal region between the Rhine and the Ems (river), Ems rivers, in what what is now the northern Netherlands. They are not mentioned in Roman records af ...
. First the rebel allies captured two Roman forts in their territory, and a cohort of
Tungri defected to Civilis. Then two legions sent against Civilis were defeated when their companion Batavi ' defected to his side.
The ''
Classis Germanica'' (Rhine flotilla), largely manned by Batavi, was seized by Civilis. Most importantly, the eight Batavi cohorts stationed at Mainz with ''XIV Gemina'' mutinied and joined him, defeating at
Bonn
Bonn () is a federal city in the German state of North Rhine-Westphalia, located on the banks of the Rhine. With a population exceeding 300,000, it lies about south-southeast of Cologne, in the southernmost part of the Rhine-Ruhr region. This ...
a Roman force that attempted to block their return to their homeland. By now, Civilis commanded at least 12 regiments (6,000 men) of Roman-trained and equipped auxiliary troops, as well as a much larger number of tribal levies. A number of German tribes from beyond the Rhine joined his cause. Several other German and Gallic units sent against him deserted, as the revolt spread to the rest of
Gallia Belgica, including the Tungri,
Lingones and
Treviri tribes. He was able to destroy the two remaining legions in Germania Inferior, (''
V Alaudae'' and ''
XV Primigenia'').
By this stage, Rome's entire position on the Rhine and even in Gaul was imperiled. Their civil war over, the Romans mustered a huge task force of eight legions (five dispatched from Italy, two from Spain and one from Britain) to deal with Civilis. Its commander
Petillius Cerialis had to fight two difficult battles, at
Trier
Trier ( , ; ), formerly and traditionally known in English as Trèves ( , ) and Triers (see also Names of Trier in different languages, names in other languages), is a city on the banks of the Moselle (river), Moselle in Germany. It lies in a v ...
and
Xanten
Xanten (, Low Rhenish: ''Santen'') is a town in the state of North Rhine-Westphalia, Germany. It is located in the district of Wesel.
Xanten is known for the Archaeological Park, one of the largest archaeological open air museums in the ...
, before he could overrun the Batavi's homeland. Tacitus' surviving narrative breaks off as he describes a meeting on an island in the Rhine delta between Civilis and Cerialis to discuss peace terms. We do not know the outcome of this meeting or Civilis' ultimate fate. But, in view of his former friendship with Vespasian, who had already offered him a pardon, and the fact that the Romans still needed the Batavi levies, it is likely that the terms were lenient by Roman standards.
Petilius Cerialis took a number of reconstituted Batavi units with him to Britain, and the Batavi regiments continued to serve with special distinction in Britain and elsewhere for the rest of the 1st century and beyond. Even as late as 395, units with the Batavi name, although long since composed of recruits from all over the empire, were still classified as elite ''
palatini'', e.g. the (cavalry) and (infantry).
Flavian era (69–96 AD)
The revolt of the Batavi appears to have led to a significant change in the Roman government's policy on deployment of Auxilia. The revolt proved that in times of civil strife, when legions were far from their bases campaigning for rival claimants to the imperial throne, it was dangerous to leave provinces exclusively in the hands of auxiliary regiments recruited from the indigenous nation. During the Julio-Claudian period, auxiliary regiments had often been deployed away from their original home province.
But in the Flavian period (69–96), this appears to have become standard policy.
Thus in AD 70, five reconstituted Batavi regiments (one ' and four ') were transferred to Britain under Petillius Cerialis, who had suppressed the Civilis revolt and then embarked on the governorship of the island. The great majority of regiments probably founded in the 1st century were stationed away from their province of origin in the second e.g. of 13 British regiments recorded in the mid-2nd century, none were stationed in Britain. Furthermore, it appears that in the Flavian era native noblemen were no longer permitted to command auxiliary units from their own tribe.
After a prolonged period in a foreign province a regiment would become assimilated, since the majority of its new recruits would be drawn from the province in which it was stationed, or neighbouring provinces.
Those same "British" units, mostly based on the Danube frontier, would by c. 150, after almost a century away from their home island, be largely composed of Illyrian, Thracian and Dacian recruits. However, there is evidence that a few regiments at least continued to draw some recruits from their original home provinces in the 2nd century e.g. Batavi units stationed in Britain.
[Mattingly (2006) 168–9]
The Flavian period also saw the first formation of large, double-size units, both infantry and cavalry, of a nominal strength of 1,000 men (), though they were actually mostly smaller (720 for an and 800 for a ).
These were the mirror image of the double-strength first cohorts of legions also introduced at this time. Such units remained a minority of the Auxilia: in the mid-2nd century, they constituted 13% of units, containing 20% of total manpower.
[Hassall (2000) 332–4]
Later Principate (97–284)
In 106 AD, emperor Trajan finally defeated the
Dacian kingdom of
Decebalus
Decebalus (; ), sometimes referred to as Diurpaneus, was the last Dacians, Dacian king. He is famous for fighting three wars, with varying success, against the Roman Empire under two emperors. After raiding south across the Danube, he defeated a R ...
and annexed it as the Roman province of
Dacia Traiana
Roman Dacia ( ; also known as ; or Dacia Felix, ) was a Roman province, province of the Roman Empire from 106 to 271–275 AD. Its territory consisted of what are now the regions of Oltenia, Transylvania and Banat (today all in Romania, excep ...
. By the mid-2nd century, there were 44 auxiliary regiments stationed there, about 10% of the total auxilia. In Britain, there were 60. Together, these two provinces contained about a quarter of the total auxiliary regiments.
There is considerable scholarly dispute about the precise size of the auxilia during the imperial era, even during the corp's best-documented period, the rule of Trajan's successor,
Hadrian
Hadrian ( ; ; 24 January 76 – 10 July 138) was Roman emperor from 117 to 138. Hadrian was born in Italica, close to modern Seville in Spain, an Italic peoples, Italic settlement in Hispania Baetica; his branch of the Aelia gens, Aelia '' ...
(117–138). This is evident if one compares calculations by Spaul (2000) and Holder (2003):
NOTE: Manpower figures exclude officers (centurions and decurions), which would have numbered about 3,500 men overall.
In addition, Holder believes that a further 14 ', which are attested under Trajan, immediately before Hadrian's rule, but not during or after it, probably continued in existence, giving a total of 381 units and 225,000 effectives. The discrepancy between the two scholars is due to: (i) Interpretation of units with the same name and number, but attested in different provinces in the same period. Spaul tends to take a more cautious approach and to assume such are the same unit moving base frequently, while Holder tends to regard them as separate units which acquired the same number due to duplicated (or even triplicated) seriation. (ii) Assumptions about how many ' were '. Spaul accepts only those ' specifically attested as ' i.e., about 40% of recorded units. Holder estimates that at least 70% of ' contained cavalry contingents by the early 2nd century.
Even according to the more conservative estimate, the auxilia were by this time significantly larger than the legions, which contained c. 155,000 effectives (28 legions of 5,500 men each) at this time, of which just 3,360 were cavalry. (For a detailed breakdown, see section 4:
Auxilia deployment in the 2nd century, below).
During the second half of the 2nd century, the Roman army underwent considerable further expansion, with the addition of five new legions (27,500 men) to a Principate peak of 33. A matching number of auxilia (i.e. c. 50 regiments, although only the names of around 25–30 have survived in the epigraphic record) were probably added, possibly reaching a peak of c. 440 regiments and around 250,000 effectives by the end of
Septimius Severus
Lucius Septimius Severus (; ; 11 April 145 – 4 February 211) was Roman emperor from 193 to 211. He was born in Leptis Magna (present-day Al-Khums, Libya) in the Roman province of Africa. As a young man he advanced through cursus honorum, the ...
's rule (211 AD).
The likely growth of the Roman auxilia may be summarised as follows:
NOTE: Regular land forces only. Excludes citizen-militias, barbarian ', and Roman navy
The naval forces of the Ancient Rome, ancient Roman state () were instrumental in the Roman conquest of the Mediterranean Basin, but it never enjoyed the prestige of the Roman legions. Throughout their history, the Romans remained a primarily land ...
effectives
During the 2nd century, some units with the new names ('group') and ('detachment') appear in the diploma record. Their size is uncertain, but was likely smaller than the regular and ', as originally they were probably detachments from the latter, acquiring independent status after long-term separation. As these units are mentioned in diplomas, they were presumably part of the regular auxiliary organisation. But was also a generic term used for barbarian units outside the regular auxilia. (see section 2.4
Irregular units, below).
In 212, the (Antonine decree) of emperor
Caracalla
Marcus Aurelius Antoninus (born Lucius Septimius Bassianus, 4 April 188 – 8 April 217), better known by his nickname Caracalla (; ), was Roman emperor from 198 to 217 AD, first serving as nominal co-emperor under his father and then r ...
granted Roman citizenship to all the free inhabitants of the Empire – the ' – thus abolishing their second-class status. But there is no evidence that the citizens-only rule for legions was also abolished at this time. The legions simply gained a much wider recruitment base, as they were now able to recruit any male free resident of the empire. Auxiliary units were now recruited mainly from Roman citizens, but probably continued to recruit non-citizen from outside the Empire's borders.
[Goldsworthy (2003) 74] However, the citizens-only rule for legions appears to have been dropped some time during the 3rd century, as by the 4th-century Romans and barbarians are found serving together in all units.
[Elton (1996) 148–52]
In the mid to late 3rd century, the army was afflicted by a combination of military disasters and of pestilence, the so-called
Crisis of the Third Century
The Crisis of the Third Century, also known as the Military Anarchy or the Imperial Crisis, was a period in History of Rome, Roman history during which the Roman Empire nearly collapsed under the combined pressure of repeated Barbarian invasions ...
. In 251–271, Gaul, the Alpine regions and Italy, the Balkans and the East were simultaneously overrun by Alamanni, Sarmatians, Goths and Persians respectively. At the same time, the Roman army was struggling with the effects of a devastating pandemic, probably of
smallpox
Smallpox was an infectious disease caused by Variola virus (often called Smallpox virus), which belongs to the genus '' Orthopoxvirus''. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (W ...
: the
Plague of Cyprian, which began in 251 and was still raging in 270, when it claimed the life of emperor
Claudius II Gothicus. The evidence for an earlier pandemic, the
Antonine Plague (also smallpox) indicates a mortality of 15–30% in the empire as a whole. The armies would likely have suffered deaths at the top end of the range, due to their close concentration of individuals and frequent movements across the empire. This probably led to a steep decline in military numbers, which only recovered at the end of the century under
Diocletian
Diocletian ( ; ; ; 242/245 – 311/312), nicknamed Jovius, was Roman emperor from 284 until his abdication in 305. He was born Diocles to a family of low status in the Roman province of Dalmatia (Roman province), Dalmatia. As with other Illyri ...
(r. 284–305).
[MacMullen (1979) 455]
The recruitment shortfall caused by the crisis seems to have led to recruitment of barbarians to the auxilia on a much greater scale than previously. By the 4th century, it has been estimated that some 25% of regular army recruits were barbarian-born. In the elite regiments, anywhere between a third and a half of recruits may have been barbarian.
This is likely a much greater proportion of foreigners than joined the auxilia in the 1st and 2nd centuries. In the 3rd century, a small number of regular auxiliary units appear in the record that, for the first time, bear the names of barbarian tribes from outside the empire e.g. the attested in 3rd-century Britain. This was probably an offshoot of the 5,500 surrendered Sarmatian horsemen posted on
Hadrian's Wall
Hadrian's Wall (, also known as the ''Roman Wall'', Picts' Wall, or ''Vallum Aelium'' in Latin) is a former defensive fortification of the Roman province of Roman Britain, Britannia, begun in AD 122 in the reign of the Emperor Hadrian. Ru ...
by emperor
Marcus Aurelius
Marcus Aurelius Antoninus ( ; ; 26 April 121 – 17 March 180) was Roman emperor from 161 to 180 and a Stoicism, Stoic philosopher. He was a member of the Nerva–Antonine dynasty, the last of the rulers later known as the Five Good Emperors ...
in c. 175. This unit may be an early example of a novel process whereby irregular units of ' () were transformed into regular auxilia. This process intensified in the 4th century: the ', a key document on the
late Roman army, lists a large number of regular units with barbarian names.
4th century

In the 4th century, the Roman army underwent a radical restructuring. In the rule of
Diocletian
Diocletian ( ; ; ; 242/245 – 311/312), nicknamed Jovius, was Roman emperor from 284 until his abdication in 305. He was born Diocles to a family of low status in the Roman province of Dalmatia (Roman province), Dalmatia. As with other Illyri ...
(284–305), the traditional Principate formations of , ' and ' appear to have been broken up into smaller units, many of which bore a variety of new names. Under
Constantine I
Constantine I (27 February 27222 May 337), also known as Constantine the Great, was a Roman emperor from AD 306 to 337 and the first Roman emperor to convert to Christianity. He played a Constantine the Great and Christianity, pivotal ro ...
(r. 312–337) it appears that military units were classified into three grades based on strategic role and to some extent quality: ''
palatini'', elite units normally part of the (imperial escort armies); , higher-grade interception forces based in frontier provinces; and , lower-grade border troops. (See
Late Roman army).
The old Principate auxilia regiments provided the basis for units at all three grades. The lists about 70 ' and ' that retained their 2nd-century names, mostly . But traces of other auxilia regiments can be found in the and armies. For example, many of the new-style infantry regiments, considered among the best units in the army, were probably formed from old-style auxiliary ', which they appear to closely resemble.
The late 4th-century writer on military affairs
Vegetius complains of contemporary young men joining the "auxilia" in preference to the "legions" to avoid the latter's tougher training and duties. But it is unclear what types of units he was referring to. It is possible that those older terms were still popularly used (misleadingly) to mean ' and respectively. In any event, his quote in no way describes accurately the Principate auxilia, many of which were of very high quality.
Unit types and structure
Regular unit types
The following table sets out the official, or establishment, strength of auxiliary units in the 2nd century. The real strength of a unit would fluctuate continually, but would likely have been somewhat less than the establishment most of the time.
* ' in original c.R. '[Birley (2002) 46]
** ' in Batavi and Tungri '
NOTE: Opinion is divided about the size of an , between 30 and 32 men. 30 was the size of a in the Republican cavalry and in the of the Principate auxilia. Against this is a statement by Arrian that an ' was 512 strong. This would make an 32 men strong.
'
These all-infantry units were modeled on the cohorts of the legions, with the same officers and sub-units. They were typically considered to be more of a
light infantry
Light infantry refers to certain types of lightly equipped infantry throughout history. They have a more mobile or fluid function than other types of infantry, such as heavy infantry or line infantry. Historically, light infantry often fought ...
than proper legionaries. Some auxiliaries may however have been equipped with the ''
lorica segmentata'', the most sophisticated legionary body armour, although scholars dispute this. Besides this possibility, monuments (like on
Trajan's Column) show auxiliaries wearing chain-mail armor, which length and form varied over the first and second century. They wore helmets similar to those of the Legion. Yet they seem to be simplified versions that where further improved over the same timeframe. They were equipped with a sword, a dagger and one or more spears or
javelin
A javelin is a light spear designed primarily to be thrown, historically as a ranged weapon. Today, the javelin is predominantly used for sporting purposes such as the javelin throw. The javelin is nearly always thrown by hand, unlike the sling ...
s. This spear might have been a ''
lancea'', which can be used as a javelin as well as a thrusting spear. Based on archeological evidences auxiliaries probably had additional lighter javelins to their . The shield of the auxiliaries was oval.
There is no evidence that auxiliary infantry fought in a looser order than legionaries.
It appears that in a set-piece battle line, auxiliary infantry would normally be stationed on the flanks, with legionary infantry holding the centre e.g. as in the
Battle of Watling Street (AD 60), the final defeat of the rebel Britons under queen
Boudicca. This was a tradition inherited from the Republic, when the precursors of auxiliary ', the Latin ', occupied the same position in the line.
[Goldsworthy (2000), p. 52] The flanks of the line required equal, if not greater, skill to hold as the centre.
'
During the
Principate
The Principate was the form of imperial government of the Roman Empire from the beginning of the reign of Augustus in 27 BC to the end of the Crisis of the Third Century in AD 284, after which it evolved into the Dominate. The principate was ch ...
period of the
Roman Empire
The Roman Empire ruled the Mediterranean and much of Europe, Western Asia and North Africa. The Roman people, Romans conquered most of this during the Roman Republic, Republic, and it was ruled by emperors following Octavian's assumption of ...
(30 BC – AD 284), the all-mounted ' ('wings') contained the elite cavalry of the army.
They were specially trained in elaborate manoeuvres, such as those displayed to the emperor Hadrian during a documented inspection in Numidia. They were best-suited for large-scale operations and battle, during which they acted as the primary cavalry escort for the legions, which had almost no cavalry of their own. Roman were normally armoured, with mail or scale body armour, a cavalry version of the infantry helmet (with more protective features, such as completely covered ears) and oval shield or hexagonal. Their weapons could be a lance, javelins, or bow and arrow but all Roman horseman had a sword (called a ) and a dagger (the ). The elite status of an is shown by the fact that he received 20% more pay than his counterpart in an auxiliary cohort or a legionary infantryman.
The favored sources of recruitment for the cavalry of the were
Gauls
The Gauls (; , ''Galátai'') were a group of Celts, Celtic peoples of mainland Europe in the Iron Age Europe, Iron Age and the Roman Gaul, Roman period (roughly 5th century BC to 5th century AD). Their homeland was known as Gaul (''Gallia''). Th ...
,
Germans
Germans (, ) are the natives or inhabitants of Germany, or sometimes more broadly any people who are of German descent or native speakers of the German language. The Basic Law for the Federal Republic of Germany, constitution of Germany, imple ...
,
Iberians and
Thracians
The Thracians (; ; ) were an Indo-European languages, Indo-European speaking people who inhabited large parts of Southeast Europe in ancient history.. "The Thracians were an Indo-European people who occupied the area that today is shared betwee ...
. All of these peoples had long-established skills and experience of fighting from horseback – in contrast to the Romans themselves. The ' were better paid and mounted than the more numerous horsemen of the (see below).
'
These were ' with a cavalry contingent attached. There is evidence that their numbers expanded with the passage of time. Only about 40% of attested ' are specifically attested as in inscriptions, which is probably the original Augustan proportion. A study of units stationed in Syria in the mid-2nd century found that many units that did not carry the ''equitata'' title did in fact contain cavalrymen e.g. by discovery of a tombstone of a cavalryman attached to the cohort. This implies that by that time, at least 70% of ' were probably '.
[Holder (2003), p. 119] The addition of cavalry to a cohort obviously enabled it to carry out a wider range of independent operations. A was in effect a self-contained mini-army.
The traditional view of (the cavalry arm of '), as expounded by G.L. Cheesman, was that they were just a mounted infantry with poor-quality horses. They would use their mounts simply to reach the battlefield and then would dismount to fight. This view is today discredited. Although it is clear that ' did not match ( cavalrymen) in quality (hence their lower pay), the evidence is that they fought as cavalry in the same way as the ' and often alongside them. Their armour and weapons were the same as for the .
Nevertheless, non-combat roles of the ' differed significantly from the '. Non-combat roles such as despatch riders () were generally filled by cohort cavalry.
Auxiliary specialised units
In the Republican period, the standard trio of specialised auxilia were Balearic slingers, Cretan archers and Numidian light cavalry. These functions, plus some new ones, continued in the 2nd-century auxilia.
Heavily-armoured lancers
, or simply for short, were the heavily armoured cavalry of the Roman army. Based on Sarmatians, Sarmatian and Parthian models, they were also known as ''Kontos (weapon), contarii'' and , although it is unclear whether these terms were interchangeable or whether they denoted variations in equipment or role. Together with new units of light mounted archers, the ' were designed to counter Parthian (and, in
Pannonia
Pannonia (, ) was a Roman province, province of the Roman Empire bounded on the north and east by the Danube, on the west by Noricum and upper Roman Italy, Italy, and on the southward by Dalmatia (Roman province), Dalmatia and upper Moesia. It ...
, Sarmatian) battle tactics. Parthian armies consisted largely of cavalry. Their standard tactic was to use light mounted archers to weaken and break up the Roman infantry line, and then to rout it with a charge by the ' concentrated on the weakest point. The only special heavy cavalry units to appear in the 2nd-century record are and stationed in Pannonia and Moesia Inferior, respectively, in the 2nd century.
Light cavalry
From the Second Punic War until the 3rd century AD, the bulk of Rome's light cavalry (apart from mounted archers from Syria) was provided by the inhabitants of the provinces of Africa (Roman province), Africa and Mauretania Caesariensis, the Numidae or Mauri (from whom derives the English term ''Moors''), who were the Berber mythology, ancestors of the
Berber people of modern Algeria and Morocco. They were known as the ''equites Maurorum'' or ('Moorish or
Numidian cavalry
Numidian cavalry was a type of light cavalry developed by the Numidians. They were used by Hannibal during the Punic Wars, and later became commonplace in the Roman army of the late Republic.
History
Numidian cavalry is first mentioned by Polybi ...
'). On Trajan's Column, Mauri horsemen, depicted with long hair in dreadlocks, are shown riding their small but resilient horses bare-back and unbridled, with a simple braided rope round their mount's neck for control. They wear no body or head armour, carrying only a small, round leather shield. Their weaponry cannot be discerned due to stone erosion, but is known from Livy to have consisted of several short javelins. Exceptionally fast and maneuverable, Numidian cavalry would harass the enemy by hit-and-run attacks, riding up and loosing volleys of javelins, then scattering faster than any opposing cavalry could pursue. They were superbly suited to scouting, harassment, ambush and pursuit. It is unclear what proportion of the Numidian cavalry were regular auxilia units as opposed to irregular ' units.
In the 3rd century, new formations of light cavalry appear, apparently recruited from the Danubian provinces: the ('Dalmatian cavalry'). Little is known about these, but they were prominent in the 4th century, with several units listed in the .
Camel troops
A unit of ('camel-mounted troops') is attested from the 2nd century, the in Syria.
Archers
A substantial number of auxiliary regiments (32, or about 1 in 12 in the 2nd century) were denoted , or archer-units (from ''sagittarii, '' , from 'arrow'). These 32 units (of which four were double-strength) had a total official strength of 17,600 men. All three types of auxiliary regiment (', and ) could be denoted . Although these units evidently specialised in archery, it is uncertain from the available evidence whether all ' personnel were archers, or simply a higher proportion than in ordinary units. At the same time, ordinary regiments probably also possessed some archers, otherwise their capacity for independent operations would have been unduly constrained. Bas reliefs appear to show personnel in ordinary units employing bows.
From about 218 BC onwards, the archers of the Roman army of the mid-Republic were virtually all mercenaries from the island of
Crete
Crete ( ; , Modern Greek, Modern: , Ancient Greek, Ancient: ) is the largest and most populous of the Greek islands, the List of islands by area, 88th largest island in the world and the List of islands in the Mediterranean#By area, fifth la ...
, which boasted a long specialist tradition. During the late Republic (88–30 BC) and the Augustan period, Crete was gradually eclipsed by men from other, much more populous, regions subjugated by the Romans with strong archery traditions. These included Thrace, Anatolia and, above all, Syria. Of the 32 units attested in the mid-2nd century, thirteen have Syrian names, seven Thracian, five from Anatolia, one from Crete and the remaining six of other or uncertain origin.
Three distinct types of archers are shown on Trajan's Column: (a) with scalar cuirass, conical steel helmet and cloak; (b) without armour, with cloth conical cap and long tunic; or (c) equipped in the same way as general auxiliary foot-soldiers (apart from carrying bows instead of javelins). The first type were probably Syrian or Anatolian units; the third type probably Thracian.
[Rossi (1971), p. 102] The standard bow used by Roman auxilia was the composite bow, recurved composite bow, a sophisticated, compact and powerful weapon.
[Goldsworthy (2003), p. 137]
Slingers
From about 218 BC onwards, the Republican army's slingers were exclusively mercenaries from the Balearic Islands, which had nurtured a Balearic slinger, strong indigenous tradition of slinging from prehistoric times. As a result, in classical Latin, (literally 'inhabitants of the Balearic Islands') became an alternative word for 'slingers' (, from 'sling'). Because of this, it is uncertain whether most of the imperial army's slingers continued to be drawn from the Balearics themselves, or, like archers, derived mainly from other regions.
Independent slinger units are not attested in the epigraphic record of the Principate.
However, slingers are portrayed on Trajan's Column. They are shown unarmoured, wearing a short tunic. They carry a cloth bag, slung in front, to hold their shot ().
Scouts/
('reconnaissance troops', from 'to scout'). Two examples include attested to in the 3rd century in Britain: and (both names of forts). It is possible, however, that more than 20 such units served in Britain. The literal translation of ' is 'numbers' and it was often used in the context of a generic title for any unit that was not of a standard size or structure. From the 2nd century onward they served as frontier guards, often supplied by the Sarmatians and the Ancient Germanic, Germans. Little else is known about such units.
Irregular allied forces
Throughout the Principate period, there is evidence of ethnic units of outside the normal auxilia organisation fighting alongside Roman troops. To an extent, these units were simply a continuation of the old client-king levies of the late Republic: ad hoc bodies of troops supplied by Rome's puppet petty-kings on the imperial borders for particular campaigns. Some clearly remained in Roman service beyond the campaigns, keeping their own native leadership, attire and equipment and structure. These units were known to the Romans as ('allies'), (from , Greek for 'allies') or ('treaty troops' from , 'treaty'). One estimate puts the number of in the time of Trajan at about 11,000, divided into about 40 ' (units) of about 300 men each. The purpose of employing ' units was to use their specialist fighting skills. Many of these would have been troops of Numidian cavalry (see Auxiliaries (Roman military)#Light cavalry, light cavalry above).
The ' make their first official appearance on Trajan's Column, where they are portrayed in a standardised manner, with long hair and beards, barefoot, stripped to the waist, wearing long trousers held up by wide belts and wielding clubs. In reality, several different tribes supported the Romans in the Dacian wars. Their attire and weapons would have varied widely. The Column stereotypes them with the appearance of a single tribe, probably the most outlandish-looking, to differentiate them clearly from the regular auxilia. Judging by the frequency of their appearance in the Column's battle scenes, the ' were important contributors to the Roman operations in Dacia. Another example of ' are the 5,500 captured Sarmatian cavalrymen sent by Emperor
Marcus Aurelius
Marcus Aurelius Antoninus ( ; ; 26 April 121 – 17 March 180) was Roman emperor from 161 to 180 and a Stoicism, Stoic philosopher. He was a member of the Nerva–Antonine dynasty, the last of the rulers later known as the Five Good Emperors ...
(r. 161–180) to garrison a fort on Hadrian's Wall after their defeat in the Marcomannic Wars.
Recruitment, ranks and pay
The evidence for auxiliary ranks and pay is scant: even less exists than the patchy evidence for their legionary counterparts. There seems to be some consensus, however, that the auxiliary was paid one third of what a legionary received: 300 sesterces a year (400 after the reign of the emperor Commodus). Both auxiliaries and seamen received the of 300 sesterces, although the various sources differ as to whether auxiliaries and sailors received the retirement bonus known as the , or honorable discharge.
The available data may be broken down and summarised as follows:
Rankers (')

At the bottom end of the rank pyramid, rankers were known as ( from the ''caligae'' or hob-nailed sandals worn by soldiers). Depending on the type of regiment they belonged to, they held the official ranks of (foot soldier in a ), (cavalryman in a ) and ( cavalryman).
During the Principate, recruitment into the legions was restricted to Roman citizens only. This rule, which derived from the pre-Social War Republican army, was strictly enforced. The few exceptions recorded, such as during emergencies and for the illegitimate sons of legionaries, do not warrant the suggestion that the rule was routinely ignored.
In the 1st century, the vast majority of auxiliary common soldiers were recruited from the Roman ''Peregrinus (Roman), peregrini'' (second-class citizens). In the Julio-Claudian era, conscription of seems to have been practiced alongside voluntary recruitment, probably in the form of a fixed proportion of men reaching military age in each tribe being drafted.
[Holder (1980) 123] From the Flavian era onwards, the auxilia were an all-volunteer force. Although recruits as young as 14 are recorded, the majority of recruits (66%) were from the 18–23 age group.
When it was first raised, an auxiliary regiment would have been recruited from the native tribe or people whose name it bore. In the early Julio-Claudian period, it seems that efforts were made to preserve the ethnic integrity of units, even when the regiment was posted in a faraway province. But in the later part of the period, recruitment in the region where the regiment was posted increased and became predominant from the Flavian era onwards.
The regiment would thus lose its original ethnic identity.
The unit's name would thus become a mere curiosity devoid of meaning, although some of its members might inherit foreign names from their veteran ancestors. This view has to be qualified, however, as evidence from military diplomas and other inscriptions shows that some units continued to recruit in their original home areas e.g. Batavi units stationed in Britain, where some units had an international membership.
It also appears that the Danubian provinces (Raetia, Pannonia, Moesia, Dacia) remained key recruiting grounds for units stationed all over the empire.
Researchers have often assumed that Roman citizens were also regularly recruited to the auxilia because various sources record auxiliary soldiers with the Tria nomina. Explanations for that phenomenon include that sons of auxiliary veterans preferred to join their fathers' old regiments, which were a kind of extended family to them, rather than join a much larger, unfamiliar legion. However, it has been shown that many of the auxiliary soldiers with tria nomina were not full Roman citizens that could enter a legion, but only had Latin citizenship or belonged (as sons of freedmen) to the "Latini Iuniani". There are, however, also instances of legionaries transferring to the auxilia (to a higher rank).
[Holder (1980) 86–8] After the grant of citizenship to all ' in 212, auxiliary regiments became predominantly citizen units.
Less clearcut is the question of whether the regular auxilia recruited (barbarians, as the Romans called people living outside the empire's borders). Although there is little evidence of it before the 3rd century, the consensus is that auxilia recruited barbarians throughout their history.
In the 3rd century, a few auxilia units of clearly barbarian origin start to appear in the record e.g. , and in Britain.
[Mattingly (2006) 223]
There existed a hierarchy of pay between types of auxiliary, with cavalry higher paid than infantry. One recent estimate is that in the time of Augustus, the annual pay structure was: () 263 , 225, and infantryman 188.
[Goldsworthy (2003) 94] The same differentials (of about 20% between grades) seem to have existed at the time of Domitian (r. 81–96).
[Hassall (2000) 336] However, Goldsworthy points out that the common assumption that rates of pay were universal across provinces and units is unproven. Pay may have varied according to the origin of the unit.
The remuneration of an auxiliary may be compared to a legionary's as follows:
Gross salary was subject to deductions for food, clothing, boots and hay (probably for the company mules). It is unclear whether the cost of armour and weapons was also deducted, or borne by the army. Deductions left the soldier with a net salary of 78 '. This sum was sufficient, on the basis of the food deduction, to amply feed an adult for a year. In 84 AD Domitian increased basic legionary pay by 33% (from 225 to 300 '): a similar increase was presumably accorded to auxiliaries, boosting their net income to 140 ', i.e. more than two food allowances. It was entirely disposable, as the soldier was exempt from the Tax per head, poll tax (), did not pay rent (he was housed in fort barracks) and his food, clothing and equipment were already deducted. It should be borne in mind that most recruits came from peasant families living at subsistence agriculture, subsistence level. To such persons, any disposable income would appear attractive. It could be spent on leisure activities, sent to relatives or simply saved for retirement.
There is no evidence that auxiliaries received the substantial cash bonuses (donativum) handed to legionaries on the accession of a new emperor and other occasions.
[Goldsworthy (2003) 96] Although irregular, these payments (each worth 75 ' to a common legionary) averaged once every 7.5 years in the early 1st century and every three years later. Duncan-Jones has suggested that may have been paid to auxiliaries also from the time of Hadrian onwards, on the grounds that the total amount of donative to the military increased sharply at that time. A very valuable benefit paid to legionaries was the discharge bonus () paid on completion of the full 25 years' service. At 3,000 ', this was equivalent to ten years' gross salary for a common legionary after the pay increase of 84 AD. It would enable him to purchase a substantial plot of land. Again, there is no indication that auxiliaries were paid a discharge bonus. For auxiliaries, the discharge bonus was the grant of Roman citizenship, which carried important tax exemptions. However, Duncan-Jones argues that the fact that service in the auxilia was competitive with the legions (deduced from the many Roman citizens that joined the auxilia) that a discharge bonus may have been paid.
Junior officers ()
Below centurion/decurion rank, junior officers in the Roman army were known as . An auxiliary cohort's ranks appear the same as in a legionary . These were, in ascending order: ('officer of the watch'), (standard-bearer for the ), (centurion's deputy) and (standard-bearer for the whole regiment, from ). In the of ' (and of '?), the decurion's second-in-command was probably known as a , responsible for horses and caparison.
[Birley (2002) 47] As in the legions, the , together with some regimental specialists, were classified in two pay-scales: ('one-and-a-half-pay men') and ''duplicarius, duplicarii'' ('double-pay men').
These ranks are probably most closely resembled by the modern ranks of corporal and sergeant respectively.
Besides combat effectives, regiments also contained specialists, the most senior of whom were or , the rest common soldiers with the status of ('exempt soldiers' i.e. exempt from normal duties). Ranking specialists included the (regimental doctor), (veterinary doctor, in charge of the care of horses, pack animals and livestock), (keeper of the armoury), and the (clerk in charge of all the regiment's records and paperwork).
Senior officers

The limited evidence on auxiliary ' and is that such officers could be directly commissioned as well as promoted from the ranks. Many appear to have come from provincial aristocracies.
[Goldsworthy (2003) 73] Those rising from the ranks could be promotions from the legions as well as from the regiment's own ranks. In the Julio-Claudian period auxiliary and ' were a roughly equal split between citizens and ', though later citizens became predominant due to the spread of citizenship among military families.
Because ' and ' often rose from the ranks, they have often been compared to warrant officers such as Sergeant major, sergeants major in modern armies. However, centurions' social role was much wider than a modern warrant officer. In addition to their military duties, centurions performed a wide range of administrative tasks, which was necessary in the absence of an adequate bureaucracy to support provincial governors. They were also relatively wealthy, due to their high salaries (see table above).
[Goldsworthy (2003) 72] However, most of the surviving evidence concerns legionary centurions and it is uncertain whether their auxiliary counterparts shared their high status and non-military role.
There is little evidence about the pay-scales of auxiliary ' and ', but these are also believed to have amounted to several times that of a .
Unlike a (who had an officer staff of six and one ), an auxiliary ' does not appear to have enjoyed the support of purely staff officers. The possible exception is an attested ('deputy'), who may have been the ' second-in-command, if this title was a regular rank and not simply an ad hoc appointment for a specific task. Also attached to the ' were the regiment's (standard-bearer for the whole unit) and (horn-blower).
Commanders
From a survey by Devijver of persons whose origin can be determined, it appears that during the 1st century, the large majority (65%) of auxiliary prefects were of Italian origin. The Italian proportion dropped steadily, to 38% in the 2nd century, and 21% in the 3rd century. From the time of emperor Claudius (r. 41–54) only Roman knights were eligible to hold command of an auxiliary regiment. This status could be obtained either by birth (i.e. if the person was the son of a hereditary Roman knight; or by attaining the property qualification (100,000 ', the equivalent of 400 years' gross salary for an auxiliary ); or by military promotion: the latter were the chief centurions of legions () who would normally be elevated to equestrian rank by the emperor after completing their single-year term as .
[Goldsworthy (2003) 65–6]
Equestrians by birth would normally begin their military careers at c. 30 years of age. An axillary had to do 25 years of service before joining the army. Commands were held in a set sequence, each held for 3–4 years: prefect of an auxiliary ', ' in a legion and finally prefect of an auxiliary '. In Hadrian's time, a fourth command was added, for exceptionally able officers, of prefect of an . Like officers senatorial rank, hereditary equestrians held civilian posts before and after their decade of military service, whereas non-hereditary officers tended to remain in the army, commanding various units in various provinces. By the 3rd century, most auxiliary prefects had exclusively military careers.
The pay of a ' of an auxiliary regiment in the early 2nd century has been estimated at over 50 times that of a (common soldier).
(This compares to a full colonel in the British Army, who is currently paid about five times a private's salary). The reason for the huge gap between the top and the bottom of the pyramid is that Roman society was far more hierarchical than a modern one. A ' was not just a senior officer. He was also a Roman citizen (which most of his men were not) and, as a member of the equestrian order, an aristocrat. The social gulf between the ' and a soldier was thus immense, and the pay differential reflected that fact.
Names, titles and decorations
Regimental names
The nomenclature of the great majority of regiments followed a standard configuration: unit type, followed by serial number, followed by name of the ' tribe (or nation) from whom the regiment was originally raised, in the Genitive case, genitive plural case e.g. ('3rd Cohort of Batavi'); ('1st Cohort of Britons'). Some regiments combine the names of two ' tribes, most likely after the merger of two previously separate regiments e.g. ('1st Wing of Pannonii and Gauls'). A minority of regiments are named after an individual, mostly after the first prefect of the regiment, e.g. (presumably named after a prefect whose middle () name was Sulpicius). The latter is also an example of a regiment that did not have a serial number.
Titles
Regiments were often rewarded for meritorious service by the grant of an honorific title. The most sought-after was the prestigious ''c.R.'' ( 'of Roman citizens') title. In the latter case, all the regiment's members at the time, but not their successors, would be granted Roman citizenship. But the regiment would retain the ''c.R''. title in perpetuity. Another common title was the name of the emperor making the award (or founding the regiment) e.g. : the ' name of Trajan (Marcus Ulpius Traianus r.98–117). Other titles were similar to those given to the legions e.g. (''p.f.'' 'dutiful and loyal').
[Goldsworthy (2003) 97]
Decorations
The Roman army awarded a variety of individual decorations () for valour to its legionaries. was a miniature spear; were large medal-like bronze or silver discs worn on the cuirass; were bracelets worn on the wrist; and torc, torques were worn round the neck, or on the cuirass. The highest awards were the ('crowns'), of which the most prestigious was the , a crown made of oak leaves awarded for saving the life of a Roman citizen in battle. The most valuable award was the , a crown made of gold awarded to the first man to scale an enemy rampart. This was awarded rarely, as such a man hardly ever survived.
There is no evidence that auxiliary common soldiers received individual decorations, although auxiliary officers did. Instead, the whole regiment was honoured by a title reflecting the type of award e.g. (awarded a torque) or (awarded bracelets). Some regiments would, in the course of time, accumulate a long list of titles and decorations e.g. .
Deployment in the 2nd century

Notes: (1) Table excludes about 2,000 officers (centurions and above). (2) Auxiliary cavalry nos. assumes 70% of ''cohortes'' were ''equitatae''
Analysis
# The table shows the importance of auxiliary troops in the 2nd century, when they outnumbered legionaries by 1.5 to 1.
# The table shows that legions did not have a standard complement of auxiliary regiments
[Goldsworthy (2000)] and that there was no fixed ratio of auxiliary regiments to legions in each province. The ratio varied from six regiments per legion in Cappadocia to 40 per legion in Mauretania.
# Overall, cavalry represented about 20% (including the small contingents of legionary cavalry) of the total army effectives. But there were variations: in Mauretania the cavalry proportion was 28%.
# The figures show the massive deployments in Britannia and Dacia. Together, these two provinces account for 27% of the total auxilia corps.
See also
*
Imperial Roman army
* Roman auxiliaries in Britain
* Structural history of the Roman military
* Veteran (Roman history)
Citations
References
Ancient
*
Arrian ''Acies contra Alanos'' (early 2nd century)
* Dio Cassius ''Roman History'' (mid-3rd century)
*
Suetonius
Gaius Suetonius Tranquillus (), commonly referred to as Suetonius ( ; – after AD 122), was a Roman historian who wrote during the early Imperial era of the Roman Empire. His most important surviving work is ''De vita Caesarum'', common ...
''De vita Caesarum'' (early 2nd century)
*
Tacitus
Publius Cornelius Tacitus, known simply as Tacitus ( , ; – ), was a Roman historian and politician. Tacitus is widely regarded as one of the greatest Roman historians by modern scholars.
Tacitus’ two major historical works, ''Annals'' ( ...
''Agricola'' (end of 1st century)
*
Tacitus
Publius Cornelius Tacitus, known simply as Tacitus ( , ; – ), was a Roman historian and politician. Tacitus is widely regarded as one of the greatest Roman historians by modern scholars.
Tacitus’ two major historical works, ''Annals'' ( ...
''Annales'' (end of 1st century)
*
Tacitus
Publius Cornelius Tacitus, known simply as Tacitus ( , ; – ), was a Roman historian and politician. Tacitus is widely regarded as one of the greatest Roman historians by modern scholars.
Tacitus’ two major historical works, ''Annals'' ( ...
''Historiae'' (end of 1st century)
* Vegetius ''De re militari'' (late 4th century)
Modern
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
External links
Roman Military Diplomas OnlineVindolanda Tablets Online
{{DEFAULTSORT:Auxiliaries (Roman Military)
Military of ancient Rome,
Roman auxiliaries, Roman auxiliaries
Military units and formations of the Roman Empire