Ystrad Tywi (, ''Valley of the Tywi'') is a region of southwest

Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...

situated on the banks of the

River Tywi The River Towy ( cy, Afon Tywi, ) is one of the longest rivers flowing entirely within Wales. Its total length is . It is noted for its sea trout and salmon fishing. Route The Towy rises within of the source of the River Teifi on the lower slo ...

and possibly the

River Loughor The River Loughor () ( cy, Afon Llwchwr) is a river in Wales which marks the border between Carmarthenshire and Swansea. The river is sourced from an underground lake at the Black Mountain emerging at the surface from Llygad Llwchwr which tran ...

. Although Ystrad Tywi was never a kingdom itself, it was historically a valuable territory and was fought over by the various kings of

Dyfed Dyfed () is a preserved county in southwestern Wales. It is a mostly rural area with a coastline on the Irish Sea and the Bristol Channel. Between 1974 and 1996, Dyfed was also the name of the area's county council and the name remains in use f ...

Deheubarth Deheubarth (; lit. "Right-hand Part", thus "the South") was a regional name for the realms of south Wales, particularly as opposed to Gwynedd (Latin: ''Venedotia''). It is now used as a shorthand for the various realms united under the House o ...

Seisyllwg Seisyllwg () was a petty kingdom of medieval Wales.Davies, p. 85 It is unclear when it emerged as a distinct unit, but according to later sources it consisted of the former Kingdom of Ceredigion plus the region known as Ystrad Tywi. Thus it cover ...

Gwynedd Gwynedd (; ) is a county and preserved county (latter with differing boundaries; includes the Isle of Anglesey) in the north-west of Wales. It shares borders with Powys, Conwy County Borough, Denbighshire, Anglesey over the Menai Strait, an ...

Morgannwg Morgannwg was a medieval Welsh kingdom formed via the merger of the kingdoms of the Kingdom of Glywysing and the Kingdom of Gwent. Formation of Morgannwg First under King Morgan the Generous (fl. ) until the end of the reign of his descendant ...

and the

Normans The Normans ( Norman: ''Normaunds''; french: Normands; la, Nortmanni/Normanni) were a population arising in the medieval Duchy of Normandy from the intermingling between Norse Viking settlers and indigenous West Franks and Gallo-Romans. ...

History

The Ystrad Tywi was part of the Demetae tribe during the Roman era, how it was founded in the post Roman era is unknown, theories suggest either Irish settlement or just land that was deemed worthless by the other Kingdoms until the Kingdom of Dyfed inherited it sometime around the late 5th Century or the early 6th Century by Aergol Lawhir. Around the year 730 Seisyll ap Clydog, king of

Ceredigion Ceredigion ( , , ) is a county in the west of Wales, corresponding to the historic county of Cardiganshire. During the second half of the first millennium Ceredigion was a minor kingdom. It has been administered as a county since 1282. Cer ...

, captured Ystrad Tywi from Rhain ap Cadwgan, king of Dyfed, and annexed it to his own kingdom. The name

was given to the new enlarged kingdom. As a result,

Brycheiniog Brycheiniog was an independent kingdom in South Wales in the Early Middle Ages. It often acted as a buffer state between England to the east and the south Welsh kingdom of Deheubarth to the west. It was conquered and pacified by the Norman ...

was once again detached from Dyfed; Ystrad Tywi had previously joined the two. In an attempt to regain the lands previously held by his father Rhodri Mawr, in 894 king

Anarawd ap Rhodri Anarawd ap Rhodri (died ) was a King of Gwynedd, referenced as " King of the Britons" in the ''Annales Cambriae'' (''The Annals of Wales''). Anarawd's father Rhodri the Great, by conquest and alleged inheritances, had become ruler of most of nor ...

of Gwynedd—together with an English force from his ally

Alfred the Great Alfred the Great (alt. Ælfred 848/849 – 26 October 899) was King of the West Saxons from 871 to 886, and King of the Anglo-Saxons from 886 until his death in 899. He was the youngest son of King Æthelwulf and his first wife Osburh, who bo ...

—laid waste to Ystrad Tywi and Ceredigion. In 920

Hywel Dda Hywel Dda, sometimes anglicised as Howel the Good, or Hywel ap Cadell (died 949/950) was a king of Deheubarth who eventually came to rule most of Wales. He became the sole king of Seisyllwg in 920 and shortly thereafter established Deheubart ...

united Seisyllwg and Dyfed to create the kingdom of the

. In medieval times Ystrad Tywi was divided into three

cantref A cantref ( ; ; plural cantrefi or cantrefs; also rendered as ''cantred'') was a medieval Welsh land division, particularly important in the administration of Welsh law. Description Land in medieval Wales was divided into ''cantrefi'', which wer ...

Cantref Mawr Cantref Mawr was a cantref in south-west Wales. It was of strategic importance in medieval Wales as the location of the main seat of the princes of Deheubarth at Dinefwr. ''Cantref Mawr'' means "The Great Cantref". Each cantref in medieval Wale ...

on the north bank; Cantref Bychan and Cantref Eginawc on the south bank of the river. Eginawc (comprising the commotes of Gŵyr, Carnywyllawn, and

Kidwelly Kidwelly ( cy, Cydweli) is a town and community in Carmarthenshire, southwest Wales, approximately northwest of the most populous town in the county, Llanelli. In the 2001 census the community of Kidwelly returned a population of 3,289, ...

) was lost to the Normans in the 11th century, and for the rest of the Middle Ages only the other two cantrefi formed Ystrad Tywi. Ystrad Tywi was transformed into the county of Carmarthen when

Edward I Edward I (17/18 June 1239 – 7 July 1307), also known as Edward Longshanks and the Hammer of the Scots, was King of England and Lord of Ireland from 1272 to 1307. Concurrently, he ruled the duchies of Aquitaine and Gascony as a vas ...

enacted the

Statute of Rhuddlan The Statute of Rhuddlan (12 Edw 1 cc.1–14; cy, Statud Rhuddlan ), also known as the Statutes of Wales ( la, Statuta Valliae) or as the Statute of Wales ( la, Statutum Valliae, links=no), provided the constitutional basis for the government of ...

in 1284 following the success of his war against

Llywelyn ap Gruffudd Llywelyn ap Gruffudd (c. 1223 – 11 December 1282), sometimes written as Llywelyn ap Gruffydd, also known as Llywelyn the Last ( cy, Llywelyn Ein Llyw Olaf, lit=Llywelyn, Our Last Leader), was the native Prince of Wales ( la, Princeps Wall ...

, Prince of Wales. Though Gŵyr had by now become part of Glamorgan, the rest of Eginawc was later restored to Ystrad Tywi, which was joined with Gwarthaf (except Efelfre) to form the modern county of

Carmarthenshire Carmarthenshire ( cy, Sir Gaerfyrddin; or informally ') is a county in the south-west of Wales. The three largest towns are Llanelli, Carmarthen and Ammanford. Carmarthen is the county town and administrative centre. The county is known as ...

In legend

In the first branch of the Four Branches of the Mabinogi, the tale ''Pwyll Pendefig Dyfed'' is told of the son of Pwyll,

Pryderi Pryderi fab Pwyll is a prominent figure in Welsh mythology, the son of Pwyll and Rhiannon, and king of Dyfed after his father's death. He is the only character to appear in all Four Branches of the Mabinogi, although the size of his role varies ...

, following his father on the throne of Dyfed and adding the three cantrefi of Ystrad Tywi and the four cantrefi of Ceredigion to his kingdom. {{authority control Medieval Wales Geography of Carmarthenshire History of Carmarthenshire River Towy