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.
In the early stages of the 8th century, Ystrad Tywi was part of Dyfed. Around 730, Seisyll ap Clydog, king of Ceredigion, acquired Ystrad Tywi from Rhain ap Cadwgan, king of Dyfed, and included it in his domain.