Around 367, the Great Conspiracy saw the troops along Hadrian's Wall mutiny, allowing the Picts to overrun the northern areas of Roman Britain (in some cases joining in), in concert with Irish and Saxon attacks on the coast. The Roman provinces seem to have been retaken by Theodosius the Elder the next year, but many Romano-Britons had already been killed or taken as slaves. In 407, Constantine III declared himself "emperor of the West" and withdrew his legions to Gaul. The Byzantine historian Zosimus () stated that Constantine's neglect of the area's defense against Irish and Saxon raids and invasions caused the Britons and Gauls to fully revolt from the Roman Empire, rejecting Roman law and reverting to their native customs. In any case, Roman authority was greatly weakened following the Visigoths' sack of Rome in 410. Medieval legend attributed widespread Saxon immigration to mercenaries hired by the British king Vortigern. The Saxon communities followed a form of Germanic paganism, driving Christian Britons back to Wales, Cornwall, and Brittany or subjugating them under kingdoms with no formal church presence.