Riothamus

Riothamus (also spelled Rigothamus, Riotimus), was a military leader and considered "King of the Brettones" (c.470). Because the name means "highest leader", some scholars have suggested it may be a title, and not a personal name.

He took part in the Roman Emperor Anthemius' campaign against Euric, king of the Visigoths. Euric defeated his attack, and Riothamus vanishes from history while retreating towards Burgundy. A letter to Riothamus from Sidonius Apollinaris, who requested support to act against troublemaking Bretons, has survived.

Riothamus has been identified with the historical King Arthur by some recent scholars (notably Ashe and Fleuriot). In any case, Riothamus' activites in Gaul may be the seed from whence grew the tradition (first recorded by Geoffrey of Monmouth in his Historia Regum Britanniae[?]) that Arthur crossed the English Channel from Britain and attacked Rome.