Ystrad Tywi
Coordinates: 51°52′05″N 4°15′18″W / 51.868°N 4.255°W Ystrad Tywi (English: Vale of [the river] Tywi) is an area of south-west Wales situated on the banks of the Tywi river as it approaches the sea to join the Bristol Channel at Carmarthen. Although Ystrad Tywi was never a kingdom itself, it was a valuable territory and was fought over by the various kings of Dyfed, Deheubarth, Seisyllwg, the Kingdom of Gwynedd, the Kingdom of Morgannwg and the Normans. The area now makes up most of the modern county of Carmarthenshire.
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, 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.
In 894 Ystrad Tywi and Ceredigion were laid waste by King Anarawd of Gwynedd together with an English force from his ally King Alfred, in an attempt to regain the lands previously held by his father Rhodri Mawr.
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.
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