Carausius

Marcus Aurelius Mausaeus Valerius Carausius (died 293) was a military commander of the Roman Empire in the 3rd century. He was a Menapian from Belgic Gaul. In 286, he commanded a fleet charged with eliminating pirates in the English Channel. However, after Emperor Maximian learned that Carausius may have kept the treasure recovered from the pirates, he ordered Carausius' execution. When learned of this order, Carausius launched a revolt declared himself emperor of the short-lived Britannic Empire, centered in Britain and northern Gaul. He held power for seven years, surviving an attempt by Maximian to retake Britain in 288 or 289. After the Western Roman Emperor Constantius Chlorus retook Gaul, Carausius was assassinated by his finance minister Allectus.

Carausius was listed in Geoffrey of Monmouth's History of the Kings of Britain (1136), and is counted as a "legendary" king of Britain. Geoffrey gave Carausius a fictional biography, claiming he was a Briton of humble birth who used the Roman Empire to gain sufficient resources to establish himself as king before dying in battle at Allectus' hand.

Carausius in "Nine Drowned Churches"
While visiting a museum in Dunwich, England, musician Alistair noticed a Roman coin from the reign of Carausius among the displays.