Ystrad Tywi
In the mid 8th century, Seisyll (king of Ceredigion) invaded, conquering Ystrad Tywi, and thus physically cleaving apart Dyfed and Brycheiniog. Rhain ap Cadwgan, great-grandson of Cloten and king of Dyfed-Brycheiniog, initially attempted to retain the union; the surviving parts were consequently known as "Rhainwg".