Constantine defeats Maxentius near Rome; according to tradition he saw a Christian sign before the battle.
Date given in the Julian calendar.
Emperors Constantine and Licinius agree on religious toleration, ending the persecution of Christians in the Roman Empire.
The first ecumenical council of Christianity, convened by Constantine, condemns Arianism and formulates the Nicene Creed.
Emperor Constantine I dedicates Constantinople as the new capital of the Roman Empire.
The Goths, many of whom had crossed the Danube fleeing the Huns, crush a Roman army and kill Emperor Valens.
Emperor Theodosius I proclaims Nicene Christianity the state religion of the Roman Empire.
The Roman Empire nearly collapses under civil wars, invasions, plague and economic crisis until Diocletian's accession.