 The man he appointed to police the Channel shores , Carausius , rebelled in 286 , causing the secession of Britain and northwestern Gaul . Maximian failed to oust Carausius , and his invasion fleet was destroyed by storms in 289 or 290 . Maximian 's subordinate , Constantius , campaigned against Carausius ' successor , Allectus , while Maximian held the Rhine frontier . The rebel leader was ousted in 296 , and Maximian moved south to combat piracy near Hispania and Berber incursions in Mauretania . When these campaigns concluded in 298 , he departed for Italy , where he lived in comfort until 305 . At Diocletian 's behest , Maximian abdicated on May 1 , 305 , gave the Augustan office to Constantius , and retired to southern Italy . 
