305–306

The Abdication of Diocletian and Constantine's Proclamation at York

In 305, under pressure from Galerius, Diocletian and Maximian abdicated. Constantius Chlorus and Galerius became the new Augusti, with Severus and Maximinus Daia as Caesars. The sons of Constantius and Maximian, Constantine and Maxentius, were passed over by the new tetrarchy.

After Constantius's death at York in 306, the army proclaimed his son Constantine emperor of Britain, Gaul and Spain. Maxentius soon seized Italy and Africa.