Carausian 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.

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.

Constantius next 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.

[12] 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.

[citation needed] 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 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.