Battle of Chrysopolis

The Battle of Chrysopolis was fought on 18 September 324 between the Roman emperors Constantine I and Licinius near Chrysopolis (modern Üsküdar), opposite Byzantium (modern Istanbul) on the Asiatic shore of the Bosphorus. The battle followed Constantine's victory at the Battle of the Hellespont, where his son Crispus destroyed the Licinian fleet. Licinius withdrew his forces from Byzantium to Chalcedon and gathered the remnants of his army, reinforced by Visigothic auxiliaries and the troops of the co-emperor Martinian.

Constantine crossed the Bosphorus into Asia Minor and marched on Chrysopolis. Licinius drew up his army with the traditional pagan standards, while Constantine advanced under the labarum. Constantine launched a direct attack that routed Licinius' troops. Ancient sources report heavy losses for Licinius, and he retreated with the survivors to Nicomedia.

The defeat ended the civil war between the two emperors. Licinius surrendered soon afterwards, was initially spared, and was later executed after being accused of treason. His son was killed the following year. Constantine became sole ruler of the Roman Empire, ending the period of the Tetrarchy. He later refounded Byzantium as Constantinople, establishing a new imperial capital.