Carausian Revolt

The Carausian Revolt (AD 286–296) was an episode in Roman history, during which a Roman naval commander, Carausius, declared himself emperor over Britain and northern Gaul. His Gallic territories were retaken by the western Caesar Constantius Chlorus in 293, after which Carausius was assassinated by his subordinate Allectus. Britain was regained by Constantius and his subordinate Asclepiodotus in 296.

Carausius, a Menapian of humble birth, rose through the ranks of the Roman military and was appointed to a naval command at Bononia (Boulogne), tasked with clearing the English Channel of Frankish and Saxon raiders. However, he was accused of collaborating with the pirates to enrich himself, and the western Augustus, Maximian, ordered him to be put to death. Carausius responded by declaring himself emperor in Britain. His forces comprised not only his fleet, augmented by new ships he had built, and the three legions stationed in Britain, but a legion he had seized in Gaul, a number of foreign auxiliary units, a levy of Gaulish merchant ships, and barbarian mercenaries attracted by the prospect of booty.

A panegyric delivered to Maximian in AD 288 or 289 refers to the emperor preparing an invasion to oust Carausius. A later panegyric to Constantius Chlorus says that this invasion failed due to bad weather, although Carausius claimed it as a military victory, and Eutropius says that hostilities were in vain thanks to Carausius's military skill, and peace was agreed.

...
Wikipedia