In the autumn of AD 286, a Menapian naval commander named Marcus Aurelius Mausaeus Carausius received word that the western emperor Maximian had ordered his execution. Rather than submit, he marshalled the Classis Britannica, crossed the Channel, and declared himself Augustus. For a decade, he governed a breakaway empire comprising Roman Britain and portions of the Gallic coast - minting high-grade silver coinage that surpassed the central empire's debased currency, building the massive coastal fortifications that still stand at Pevensey and Portchester, quoting Virgil in his coin exergues, and calling Diocletian and Maximian his brothers on a diplomatic coinage whose audacity has no parallel in the numismatic record of the period. This book is the definitive account of the Carausian revolt and the Tetrarchic reconquest that ended it. Drawing on the latest numismatic research, archaeological evidence, and reassessment of the hostile literary tradition, Fredo McCormack reconstructs a decade of alternative Roman governance whose sophistication has been buried for seventeen centuries beneath the panegyrists' rhetoric of tyranny and piracy. He traces the revolt's origins in the crisis of the third century, the administrative achievement of the breakaway state, the siege of Gesoriacum, the invasion of AD 296, and the Diocletianic reorganisation whose consequences shaped Roman Britain until the collapse of imperial rule in the early fifth century. The emperor who was never emperor left better coins, better walls, and a more revealing legacy than Rome wished to acknowledge.