Seysill an Cleedog

Seisill was the son and heir of King Ceredigion Klidog ap Artluis .

In 720, he attacked nearby Dyved and conquered a large part of it, called Istrad Tiwi . The resulting state, which was approximately twice the size of Ceredigion, was later named after Seysillug in honor of Seysilla. But later historians point out that this name can be found in later medieval documents and that the kingdom is mentioned in several modern sources.

In 740, Seisill died and his son Arten became king of Seysilluga , who ruled until his death - the year 807.

• Wendy Davies, Early Medieval Wales (Prifysgol Caerlyr, 1982).
• Koch, John T. (2006). Celtic Culture: A Historical Encyclopedia. ABC-CLIO.
• Lloyd, John Edward (1912). From the Earliest Times to the Edwardian Conquest. Longmans, Green, and Co.

• Seisyll, King of Seisyllwg
• Bartrum, Peter C. A Welsh Classical Dictionary: People in History up to about AD1000 . National Library of Wales, 1993. p.28.