Latin: Flavius Claudius Constantinus
Reign: 407-411 AD
Died: Before September 18, 411
Constantine III was a general in the Roman army who served in Britain. He is sometimes referred to as Constantine III of Britain. His exact origins and early life are not well-documented.
In 407 AD, Constantine III revolted against the Western Roman Emperor Honorius. He declared himself emperor in Britain and quickly gained the support of the Roman legions stationed there, as well as some support from parts of Gaul (modern-day France).
He effectively ruled over a breakaway Western Roman Empire that included Britain, Gaul, and parts of Hispania (modern-day Spain). His reign was primarily focused on consolidating his power and trying to secure recognition from the Eastern Roman Empire (Byzantine Empire).
Constantine III’s declaration of independence led to conflict with Honorius, who was the reigning Western Roman Emperor based in Italy. Honorius, with the support of his general Stilicho, fought against Constantine III’s forces. In 411 AD, Constantine’s forces captured the city of Arles in Gaul. This was a significant achievement for his regime, as it provided him with control over an important administrative and strategic center.
However, his rule was short-lived. His support began to wane, and in 411 AD, he was betrayed and captured by a Visigothic king named Sarus, who handed him over to Honorius. Constantine III was subsequently executed.
He 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.”
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138
Triads of the Island of Britain (Welsh ”Triads”) | 11th century to 14th century