Ystrad Tywi
Charles-Edwards argues that Hyfaidd was responsible for consolidating the lands that would later become Deheubarth, annexing Ystrad Tywi and possibly Ceredigion to Dyfed before his death. He was said to have oppressed the clerics of Meneva (modern St. David's) and exiled Bishop Nobis, earning him the enmity of Nobis's kinsman, the historian Asser.