Carausian Revolt The Carausian Revolt ( 286 – 296 AD ) 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 . Revolt . 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 288 or 289 AD 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 . Carausius began to entertain visions of legitimacy and official recognition . He minted his own coins and brought their value into line with Roman issues as well as acknowledging and honouring Maximian and then Diocletian . He appears to have appealed to native British dissatisfaction with Roman rule : he issued coins with legends such as " Restitutor Britanniae " ( Restorer of Britain ) and " Genius Britanniae " ( Spirit of Britain ) . Previously , Britain had been part of the Gallic Empire established by Postumus in 260 , which had also included Gaul and Hispania and had only been restored by Aurelian in 274 . A milestone from Carlisle with his name on it suggests that the whole of Roman Britain was in Carausius ' grasp . Recovery of the Empire . In 293 Constantius Chlorus , now the western Caesar , isolated Carausius by retaking the territory he held in Gaul . He besieged the port of Bononia , building a mole across the harbour mouth to prevent the rebels from escaping by sea and ensure they could not receive maritime aid , and invaded Batavia in the Rhine delta , securing his rear against Carausius ' s Frankish allies . However , it was impossible to mount an invasion of Britain until a suitable fleet could be built . Carausius , who had been in power for seven years , was assassinated by his subordinate Allectus , who assumed command . Three years later , in 296 , the reconquest of Britain began . With Maximian holding the Rhine frontier , Constantius divided his fleet into several divisions . He led one division himself from Bononia ; another , sailing from Le Havre , was commanded by Asclepiodotus , prefect of the Praetorian Guard . They set sail in poor weather , but fog allowed Asclepiodotus ' s ships to pass Allectus ' s fleet , stationed at the Isle of Wight , unseen . They landed in the vicinity of Southampton and burned their ships . The rebels were forced to retreat from the coast , but in doing so , fell into the hands of another division and were routed . Allectus himself was killed in the battle , having removed all insignia in the hope that his body would not be identified . Archaeology suggests that Calleva Atrebatum ( Silchester ) was the site of his defeat . A group of Roman troops , who had been separated from the main body by the fog during the channel crossing , caught up with the remnants of Allectus ' s men , mostly Franks , at Londinium ( London ) , and massacred them . Constantius himself , it seems , did not reach Britain until it was all over , and the panegyrist claims he was welcomed by the Britons as a liberator . Medieval British legend . Carausius , Allectus , Asclepiodotus and Constantius appear in Geoffrey of Monmouth ' s " Historia Regum Britanniae " ( 1136 ) in distorted guise , as rulers of Britain . Here , Carausius is a native Briton who persuades the Romans to give him a naval command , and uses that to overthrow the king of Britain , Bassianus , or Caracalla . The Romans send Allectus with three legions to remove him , but Allectus proves an oppressive ruler , and Asclepiodotus , here a duke of Cornwall , leads a popular uprising to depose him . He defeats Allectus near London , and besieges his last legion in the city . The Romans surrender on the condition they are allowed safe passage out of Britain , which Asclepiodotus grants , but his allies the Venedoti behead them and throw their heads in the river Gallobroc . Ten years later Asclepiodotus is deposed by Coel , duke of Colchester , for his part in the persecution of Christians under Diocletian . The Romans send Constantius to negotiate with him . Coel agrees to pay tribute to Rome and gives Constantius his daughter Helena in marriage , and upon his death Constantius becomes the new king of Britain .