A glacis (, ) in

military engineering Military engineering is loosely defined as the art, science, and practice of designing and building military works and maintaining lines of military transport and military communications. Military engineers are also responsible for logistics b ...

is an artificial slope as part of a medieval castle or in early modern fortresses. They may be constructed of earth as a temporary structure or of stone in more permanent structure. More generally, a glacis is any slope, natural or artificial, which fulfils the above requirements. The etymology of this French word suggests a slope made dangerous with ice, hence the relationship with ''

glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

''. A ''glacis plate'' is the sloped front-most section of the hull of a

tank A tank is an armoured fighting vehicle intended as a primary offensive weapon in front-line ground combat. Tank designs are a balance of heavy firepower, strong armour, and battlefield mobility provided by tracks and a powerful engine; ...

or other

armoured fighting vehicle An armoured fighting vehicle (British English) or armored fighting vehicle (American English) (AFV) is an armed combat vehicle protected by vehicle armour, armour, generally combining operational mobility with Offensive (military), offensive a ...

Ancient fortifications

A glacis could also appear in ancient fortresses, such as the one the

ancient Egypt Ancient Egypt () was a cradle of civilization concentrated along the lower reaches of the Nile River in Northeast Africa. It emerged from prehistoric Egypt around 3150BC (according to conventional Egyptian chronology), when Upper and Lower E ...

ians built at Semna in

Nubia Nubia (, Nobiin language, Nobiin: , ) is a region along the Nile river encompassing the area between the confluence of the Blue Nile, Blue and White Nile, White Niles (in Khartoum in central Sudan), and the Cataracts of the Nile, first cataract ...

. Here it was used by them to prevent enemy

siege engine A siege engine is a device that is designed to break or circumvent heavy castle doors, thick city walls and other fortifications in siege warfare. Some are immobile, constructed in place to attack enemy fortifications from a distance, while othe ...

s from weakening

defensive wall A defensive wall is a fortification usually used to protect a city, town or other settlement from potential aggressors. The walls can range from simple palisades or earthworks to extensive military fortifications such as curtain walls with t ...

Hillforts in Britain Hillforts in Britain refers to the various hillforts within the island of Great Britain. Although the earliest such constructs fitting this description come from the Neolithic British Isles, with a few also dating to later Bronze Age Britain, Briti ...

started to incorporate glacis around 350 BC. Those at Maiden Castle, Dorset were high.

Medieval fortifications

Glacises, also called taluses, were incorporated into medieval fortifications to strengthen the walls against undermining, to hamper escalades and so that missiles dropped from the battlements would ricochet off the glacis into attacking forces. Towards the end of the medieval period some castles were modified to make them defensible against cannons. Glacis consisting of earthen slopes faced with stones were placed in front of the curtain walls and bastions (towers) to absorb the impact of cannon shots or to deflect them. Towers were lowered to the same height as the curtain walls and converted into gun platforms.

Early modern European fortifications

Early modern European fortresses were so constructed as to keep any potential assailant under the fire of the defenders until the last possible moment. On natural, level ground, troops attacking any high work have a degree of shelter from its fire when close up to it; the glacis consists of a slope with a low grade inclined towards the top of the wall. This gave defenders a direct line of sight into the assaulting force, allowing them to efficiently sweep the field with fire from the

parapet A parapet is a barrier that is an upward extension of a wall at the edge of a roof, terrace, balcony, walkway or other structure. The word comes ultimately from the Italian ''parapetto'' (''parare'' 'to cover/defend' and ''petto'' 'chest/brea ...

. Additionally, but secondarily, the bank of earth would shield the walls from being hit directly by cannon fire. Though defenders on high ground already have a direct line of sight, a glacis allows the

field of fire The field of fire or zone of fire (ZF) of a weapon, or group of weapons, is the area around it that can easily and effectively be reached by projectiles from a given position. Field of fire The term originally came from the ''field of fire'' in f ...

to be swept more efficiently by minimizing changes to the angle of their guns while firing. Furthermore, the glacis prevents attacking cannon from having a clear shot at the walls of a fortress, as usually these cannot be seen until the glacis is crossed and the ditch, bounded on either side by the smooth, masoned scarp and counterscarp, is reached.

Armored vehicles

The term ''glacis plate'' describes the sloped front-most section of the hull of a

or other armored fighting vehicle, often composed of upper and lower halves. In a head-on-head armored engagement, the glacis plate is the largest and most obvious target available to an enemy gunner.

Sloped armour Sloped armour is armour that is oriented neither Vertical and horizontal, vertically nor horizontally. Such angled armour is typically mounted on tanks and other armoured fighting vehicles (AFVs), as well as Naval ship, naval vessels such as battl ...

has two advantages: many projectiles will deflect rather than penetrate; those that attempt to will have to travel on a longer diagonal route through any given thickness of armor than if it were perpendicular to their trajectory.

Anti-tank mine An anti-tank or AT mine is a type of land mine designed to damage or destroy vehicles including tanks and armored fighting vehicles. Compared to anti-personnel mines, anti-tank mines typically have a much larger explosive charge, and a fuze desi ...

s that employ a tilt-rod fuze are also designed to detonate directly underneath the glacis plate. As a result, it is generally the thickest, most robust armored section of a tank, followed by the turret face and gun mantlet.

Gallery

File:Maiden Castle, Dorchester..jpg, Iron Age ramparts and ditches in Maiden Castle. File:Montlouis fort1.JPG, Glacis, Mont-Louis Fortress,

Pyrénées-Orientales Pyrénées-Orientales (; ; ; ), also known as Northern Catalonia, is a departments of France, department of the Regions of France, region of Occitania (administrative region), Occitania, Southern France, adjacent to the northern Spain, Spanish ...

, France

References

Bibliography

* * * * {{Fortifications Fortification (architectural elements) Vehicle armour