Sisillius I
{{Infobox royalty
| name = Sisillius I
| succession = King of Britain
| reign = c. 753 BC
| predecessor = Gurgustius
| successor = Jago
| issue = Kimarcus
| father = Gurgustius
}}
Sisillius I (Welsh: Seisyll) was a legendary king of the Britons as accounted by Geoffrey of Monmouth. He came to power in 753 BC.{{Cite web |title=Bretons |url=http://www.monarchie-noblesse.net/angleterre/bretons/bretons.htm |access-date=2024-08-25 |website=www.monarchie-noblesse.net}}
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).[http://freepages.genealogy.rootsweb.com/~jamesdow/s000/f206720.htm Tree: Seisyll (Sisillius I) (King) in BRITAIN] 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 {{lang|la|Historia Regum Britanniae}}, Sisillius is succeeded by Jago, who the Latin text describes as "{{lang|la|Iago Gurgustii nepos}}". This is generally interpreted as meaning "Jago, Gurgustius's nephew", but could mean "Jago, Gurgustius's grandson" instead.{{cite book | first=Ben | last=Guy | chapter=The Pedigrees of the Kings of Gwynedd | title=Medieval Welsh Genealogy: An Introduction and Textual Study | year=2020 | isbn=978-1-78327-513-7 | publisher=Boydell Press | series=Studies in Celtic History | chapter-url=https://archive.org/details/medieval-welsh-genealogy-book/page/262 | page=262 }}
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).
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Notes
{{s-start | noclear = true }}
{{s-reg | leg }}
{{s-bef | before = Gurgustius }}
{{s-ttl | title = King of Britain }}
{{s-aft | after = Jago }}
{{s-end}}
{{Geoffrey of Monmouth}}
{{DEFAULTSORT:Sisillius 01}}