Siege of Byzantium (324)

Siege of Byzantium
Part of Civil wars of the Tetrarchy
Left: bust of Licinius in Kunsthistorisches Museum, Vienna; right: head of the colossal statue of Constantine I in the Palazzo dei Conservatori, Rome.
Date 324 AD Location Byzantium (modern Istanbul) Result Constantinian victory
Belligerents
Constantine I	Licinius
Commanders and leaders
Constantine the Great	Licinius

The siege of Byzantium was carried out some time between July and September 324 by the forces of the Roman emperor Constantine I (r. 306–337) during his Second Civil War against his rival, co-emperor Licinius (r. 308–324). It would have been started simultaneously with the naval battle of the Hellespont (today known as Dardanelles) in which Constantine's son and caesar Crispus (r. 317–326) defeated the Lycinian navy commanded by Admiral Abanto.

The victory on the Hellespont made it possible to prolong the siege of Byzantium and forced Licinius to summon the forces that were quartered in the city to Asia Minor, where the emperor intended to regroup his remaining forces to confront Constantine again. However, he would be defeated at the consecutive battle of Chrysopolis, ending the Tetrarchy system and allowing the Constantine to establish himself as sole ruler of the Roman Empire.

This was the tenth significant siege of the city, and there were to be many more.