 Maximian soon heard that Carausius was waiting until the pirates had finished plundering before attacking and keeping their booty himself instead of returning it to the population at large or into the imperial treasury . Maximian ordered Carausius ' arrest and execution , prompting him to flee to Britain . Carausius ' support among the British was strong , and at least two British legions ( II Augusta and XX Valeria Victrix ) defected to him , as did some or all of a legion near Boulogne ( probably XXX Ulpia Victrix ) . Carausius quickly eliminated the few remaining loyalists in his army and declared himself Augustus . 
