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.