November 11
Galerius calls a council to discuss the disruptive western provinces. Diocletian and Maximian attend. Maximian is forced to abdicate and Constantine the Great is demoted to Caesar under the new Augustus Licinius.
December
Constantine the Great forges an alliance with Licinius, giving him his sister Constantia in marriage.
February
Constantine the Great and Licinius meet in Milan to cement their marriage alliance. The two emperors sign the Edict of Milan, promising religious tolerance.
Constantine the Great defeats Licinius at the Battle of Cibalae.
Constantine the Great and Licinius fight at the Battle of Mardia, where both sides take heavy losses. They agree to promote Crispus, Constantine II, and Licinius II to Caesars.
Licinius goes against the Edict of Milan and begins removing Christians from office.
The fleet of Constantine I takes moorage at Elaios against Licinius.
July 3
Licinius is soundly defeated by Constantine the Great at the Battle of Adrianople.
July
Crispus, the son of Constantine the Great, achieves a huge naval victory over Licinius at the Battle of the Hellespont.
September 18
Constantine the Great defeats Licinius at the Battle of Chrysopolis. Licinius surrenders and are sent to live as private citizens.
Licinius is accused of a plot to kill Constantine the Great and is executed.