Around AD 286–287, during the reigns of Diocletian and Maximian, a Roman naval commander named Carausius established his own imperial regime in Britain. His rise to power began with his appointment to command a fleet tasked with stopping Frankish and Saxon piracy along the coasts of northern Gaul and the English Channel. According to ancient accounts, he was accused of allowing these pirates to carry out their raids before intercepting them and keeping the recovered treasure for himself. When Maximian reportedly ordered his execution, he rebelled.

Carausius presented himself as a legitimate Roman emperor, adopting traditional imperial titles and issuing coinage that closely mimicked those of Rome. His efforts to gain recognition from Diocletian and Maximian are particularly evident in a series of coins which depicts all three rulers together, accompanied by the inscription CARAUSIUS ET FRATRES SUI, meaning "Carausius and his brothers."

However, neither Diocletian nor Maximian formally recognized his authority. Carausius maintained his position in Britain for approximately seven years before being assassinated in AD 293 by Allectus, one of his senior officials, who succeeded him as ruler. Roman authority was eventually restored in Britain in AD 296 following the successful campaign of Constantius Chlorus.