It is assumed to have been named for Seisyll, King of Ceredigion in the 7th or early 8th century, and as such he is traditionally regarded as its founder.
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It is evidently named after Seisyll, king of Ceridigion in the 7th or early 8th century, but it is unknown if he was directly responsible for its establishment.
Seisyll |
According to some genealogies, Seisyll and his son were associated with Rhuddlan, perhaps as lords of its commote in Rhos cantref.
Seisyll ap Dyfnwal is best known for being an unwitting victim of the Norman Baron, William de Braose, 3rd Lord of Bramber, who had him murdered in cold blood on or very near Christmas Day 1175 at Abergavenny Castle.