Hillside and bog above the source of the Tywi - geograph

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

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

situated on both banks of the River Towy (), it contained places such as Cedweli, Carnwyllion, Loughor, Llandeilo, and Gwyr (although this is disputed). Although Ystrad Tywi was never a kingdom itself, it was historically a valuable territory and was fought over by the various kings of Dyfed, Deheubarth, Seisyllwg,

Gwynedd Gwynedd () is a county in the north-west of Wales. It borders Anglesey across the Menai Strait to the north, Conwy, Denbighshire, and Powys to the east, Ceredigion over the Dyfi estuary to the south, and the Irish Sea to the west. The ci ...

, Morgannwg and the

Normans The Normans (Norman language, Norman: ''Normaunds''; ; ) were a population arising in the medieval Duchy of Normandy from the intermingling between Norsemen, Norse Viking settlers and locals of West Francia. The Norse settlements in West Franc ...

History

At the start of the 8th century Ystrad Tywi was part of the kingdom of Dyfed. Around the year 730 Seisyll ap Clydog, king of

Ceredigion Ceredigion (), historically Cardiganshire (, ), is a Principal areas of Wales, county in the West Wales, west of Wales. It borders Gwynedd across the River Dyfi, Dyfi estuary to the north, Powys to the east, Carmarthenshire and Pembrokeshire t ...

, captured Ystrad Tywi from Rhain ap Cadwgan, king of Dyfed, and annexed it to his own kingdom. The name Seisyllwg was given to the new enlarged kingdom. As a result, Brycheiniog 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 of Gwynedd—together with a Wessex force from his ally

Alfred the Great Alfred the Great ( ; – 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 both died when Alfr ...

—raided both Ystrad Tywi and Ceredigion. In 920 Hywel Dda united Seisyllwg and Dyfed to create the kingdom of the Deheubarth. In medieval times Ystrad Tywi was divided into three cantrefi. Cantref Mawr on the north bank; Cantref Bychan and Cantref Eginawc on the south bank of the river. Eginawc (comprising the commotes Gŵyr, Carnwyllion and Kidwelly) which was fought over many times between the Welsh and 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 King Edward I enacted the Statute of Rhuddlan in 1284 following the success of his war against Llywelyn ap Gruffudd, 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 (; or informally ') is a Principal areas of Wales, county in the South West Wales, south-west of Wales. The three largest towns are Llanelli, Carmarthen and Ammanford. Carmarthen is the county town and administrative centre. ...

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, 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.

References

Medieval history of Wales Geography of Carmarthenshire History of Carmarthenshire River Towy {{coord, 51.868, -4.255, display=title, region:GB_scale:10000