Sisillius I ('' Welsh:'' Seisyll) was a legendary king of the

Britons British people or Britons, also known colloquially as Brits, are the citizens of the United Kingdom, the British Overseas Territories, and the Crown dependencies.: British nationality law governs modern British citizenship and nationality, w ...

as accounted by

Geoffrey of Monmouth Geoffrey of Monmouth (; ; ) was a Catholic cleric from Monmouth, Wales, and one of the major figures in the development of British historiography and the popularity of tales of King Arthur. He is best known for his chronicle '' The History of ...

. He came to power in 753 BC. He was preceded by Gurgustius and succeeded by Jago. He was the father of Kimarcus, who became king of the Britons after Jago, and shares his name with one of the sons of Ebraucus, and two later kings of the same name ( Sisillius II and Sisillius III).Tree: Seisyll (Sisillius I) (King) in BRITAIN
/ref> Geoffrey has nothing to say of him beyond this.Geoffrey of Monmouth: ''The History of the Kings of Britain : an Edition and Translation of De Gestis Britonum (Historia Regum Britanniae)'', Boydell & Brewer, 1 Jan 2007, p.44.

Relation to Jago

In the , Sisillius is succeeded by Jago, who the Latin text describes as "". This is generally interpreted as meaning "Jago, Gurgustius's nephew", but could mean "Jago, Gurgustius's grandson" instead. As a result, most later sources assume that Jago was Sisillius' cousin, but the Black Book of Basingwerk, following the latter interpretation, called Jago the son of Sisillius (and so grandson of Gurgustius through Sisillius).

Notes

{{DEFAULTSORT:Sisillius 01 Legendary British kings