Constantine III

Latin: Flavius Claudius Constantinus
Died before September 18, 411

A Roman general who, in 407, declared himself Western Roman Emperor in Britain, and lived in Gaul.

He is also known as Constantine II of Britain and is confused with Geoffrey of Monmouth’s Constantine, found in Historia Regum Britanniae. Geoffrey’s Constantine becomes the grandfather of Arthur, through his son Uther Pendragon. Some sources claims that Constantine III is the grandfather of Arthur. The Welsh Triads tells us that Arthur’s grandfather is “Custennin the Blessed”, also “Bran son of Dyfnwal and Custennin son of Elen had been emperors in Rome”.

In Arthurian tradition he succeeded king Gracianus Municeps (Gratian) when the latter was assassinated. In some versions, his seneschal was Vortigern.


Sources
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138
Triads of the Island of Britain (Welsh ”Triads”) | 11th century to 14th century