Ystrad Tywi is a region of southwest Wales situated on both banks of the River Towy, it contained places such as Cedweli, Carnwyllion, Loughor, Llandeilo, and Gwyr. 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, Morgannwg and the Normans.