0308-11-11 The Congress of Carnuntum: Attempting to keep peace within the Roman Empire, the leaders of the Tetrarchy declare Maxentius and Licinius to be Augusti, while rival contender Constantine I is declared Caesar of Britain and Gaul.
0312-10-27 Roman Emperor Constantine the Great is said to have received his famous Vision of the Cross
0312-10-28 Emperor Constantine the Great beats rival Maxentius at the Battle of the Milvian Bridge
0314-10-08 Battle at Cibalae: Roman emperor in the west Constantine beats emperor in the east Licinius
0317-03-01 Crispus and Constantine II, sons of Roman Emperor Constantine I, and Licinius the younger, son of Emperor Licinius, raised to rank of Caesar
0321-03-07 Roman Emperor Constantine I decrees that the dies Solis Invicti (sun-day) is the day of rest in the Empire
0324-07-03 Battle of Adrianople: Roman Emperor Constantine I defeats his co-emperor Licinius, who flees to Byzantium