Licinius, 250–325, Roman emperor. He became coemperor with Galerius, being given the rule of Illyricum (308); after the death of Galerius he added Greece and Thrace to his territories. He allied himself with Constantine I and defeated Maximin in 313, thus becoming sole ruler in the East. He subsequently quarreled with Constantine, who defeated him (314) and forced him to cede all his European territories except for Thrace. War was resumed in 324, and Constantine defeated Licinius at Adrianople and Chrysopolis. Licinius was imprisoned and eventually put to death.