- Source: Sisillius
Sisillius (Welsh: Saessyllt) was the name of three legendary Kings of the Britons as accounted by Geoffrey of Monmouth:
Sisillius, one of the younger sons of Ebraucus
Sisillius I, successor of King Gurgustius
Sisillius II, son of King Guithelin and Queen Marcia
Sisillius III, successor of King Oenus