Ystrad Tywi (, ''Valley of the

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 sl ...

'') is a region of southwest

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

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 trans ...

. 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 of ...

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 covere ...

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, and C ...

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 I ...

and the

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

History

The Ystrad Tywi was part of the

Demetae The Demetae were a Celtic people of Iron Age and Roman period, who inhabited modern Pembrokeshire and Carmarthenshire in south-west Wales, and gave their name to the county of Dyfed. Classical references They are mentioned in Ptolemy's ''Geograp ...

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 Aergol Longhand (Modern Welsh: ''Aergol Lawhir''; c. 437 c. 515) was a legendary king of Dyfed and son and heir of King Triffyn Farfog. His name is the Welsh form of the Latin Agricola, just as his father's 'name' is the Cambrian form of "tribun ...

. Around the year 730

Seisyll ap Clydog Seisyll ap Clydog was King of Ceredigion in Wales some time in the late 7th or early 8th century. He gave his name to the later kingdom of Seisyllwg, which consisted of Ceredigion plus the region known as Ystrad Tywi; as such he was possibly the ki ...

, 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. Cere ...

, captured Ystrad Tywi from

Rhain ap Cadwgan Rhain ap Cadwgan ( en, Regin son of Cadogan; died c. 740) was an 8th-century king of Dyfed and Brycheiniog in Wales of the Early Middle Ages. He succeeded his father Cadwgan, who succeeded his father Caten ap Cloten. Biography Rhain's great-gr ...

, 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 Normans be ...

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 Rhodri ap Merfyn ( 820 – 873/877/878), popularly known as Rhodri the Great ( cy, Rhodri Mawr), succeeded his father, Merfyn Frych, as King of Kingdom of Gwynedd, Gwynedd in 844. Rhodri annexed Kingdom of Powys, Powys c. 856 and Seisyllwg c. 8 ...

, 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 north ...

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 bot ...

—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 Deheubarth ...

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 were ...

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 A commote (Welsh ''cwmwd'', sometimes spelt in older documents as ''cymwd'', plural ''cymydau'', less frequently ''cymydoedd'')''Geiriadur Prifysgol Cymru'' (University of Wales Dictionary), p. 643 was a secular division of land in Medieval Wales ...

and

Cantref Eginawc A commote ( Welsh ''cwmwd'', sometimes spelt in older documents as ''cymwd'', plural ''cymydau'', less frequently ''cymydoedd'')''Geiriadur Prifysgol Cymru'' (University of Wales Dictionary), p. 643 was a secular division of land in Medieval Wale ...

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, inc ...

) 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 vassal o ...

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