After the death of
Galerius in AD 311, there remained four emperors in the
Roman world:
Constantine I, who controlled
Gaul,
Spain, and
Britain;
Maxentius, in
Africa and
Italy;
Maximinus Daza in Roman Asia and
Egypt; and
Licinius in
Macedonia,
Greece, and
Illyricum. The expansionist ambitions of Maxentius and Maximinus led to a bellicose alliance of these princes against Constantine and Licinius, with the understanding that Maxentius would conquer the western provinces of
Europe, and Maximinus the east. Constantine, sensing the threat, in turn drew closer to Licinius, and having assured himself of the latter's overt neutrality and secret support, unexpectedly attacked Maxentius in 312. Constantine invaded Italy and defeated Maxentius in a lightning campaign which culminated in the
battle of the Milvian Bridge where the latter was killed. Meanwhile, Maximinus, on the basis of his agreement with Maxentius, had been mobilizing for war, though he concealed his intentions from Licinius with carefulness and success; as soon as his forces were prepared, though it was the middle of winter, he marched hurriedly with his army of 70,000 men through Anatolia from Antioch, arriving opposite
Byzantium while the Illyrian emperor was still at Milan. Maximinus' anxiety to catch Licinius unprepared had led to much equipment, not to mention morale, being lost in the winter march through the harsh provinces of Asia-Minor. As soon as Licinius received news of the enemy's attack, Licinius hastened from Milan to meet the invasion, assembling the resources of Illyria in his hurried course through the province. ==Battle==