officer in the Roman military service who created a short-lived independent state in Britain.

Born in Menapia, a district between the Scheldt and Meuse rivers (now in Belgium), Carausius was a pilot by profession. He had won honour in the Roman war against the Bagaudae. About AD 285, Maximian, coruler with the emperor Diocletian, had assembled a naval force to counter the Franks and Saxons who were then plundering the coasts of Spain and Gaul. Carausius was given command of this fleet, which was based at Gesoriacum (modern Boulogne).

Carausius was accused of waiting until after the pirates had carried out raids, then attacking them and seizing their cargoes for himself. Enraged by this, Maximian ordered Carausius's death, but Carausius escaped with his troops into Britain, where he set himself up as ruler, with the title of Augustus. He trained the local barbarians as sailors and soon controlled the western sea and ruled Gaul as far as Rotomagus (modern Rouen).

Carausius was, of course, maligned by imperial chroniclers. Diocletian and Maximian failed in several attempts to dislodge him and acknowledged him as ruler of Britain in 290. Constantius I drove Carausius from Gesoriacum, his European base, in 293, and that same year Carausius was slain by his finance minister, Allectus, who succeeded him for three years.