5 – Constantine Becomes Sole Emperor
The accord between the two emperors didn’t last long. Constantine appointed Bassianus, his brother-in-law, as Caesar, with authority in the Danubian provinces and Italy. Licinius saw Bassianus as a puppet and was angry that such a man could take control of his military provinces in the Balkans. He persuaded Bassianus to rebel against Constantine in 314 or 315 but not only did his enemy easily suppress the revolt, he knew Licinius was involved, and the relationship between the two men broke down.
They both took time out to prepare their respective armies, but in 316, they fought in Pannonia where Constantine emerged victorious despite a numerical disadvantage. Licinius decided to name Aurelius Valerius Valens as the new emperor of the west; a failed attempt to undermine the authority of his rival. After an indecisive battle in Thrace, the two men signed a treaty in 317 at Serdica.
Licinius agreed to surrender all Balkan and Danubian provinces to Constantine barring Thrace but retained control over his remaining eastern territories. He also agreed to execute Valens. Finally, they agreed to name three new Caesars; Licinius the Younger (Licinius’ son) and two of Constantine’s sons, Constantine II and Crispus. The empire enjoyed a short spell of peace, but war broke out again when Licinius started persecuting Christians in 320. In defiance of the treaty at Serdica, Licinius appointed himself and two of his sons as consuls in 322. Constantine responded by appointing his son Constantius II as consul in 323.
In the same year, he broke the agreement by marching on Licinius’ Thracian territory, and his enemy declared war in 324. Constantine quickly gained the advantage with victory at Adrianople followed by a major naval victory. Licinius retreated to Asia Minor and was pursued by his enemy. Constantine won another important battle at the Hellespont before the two emperors fought one last time at the pivotal Battle of Chrysopolis on September 18, 324.
Constantine arrived at the battlefield first and retired to his tent to seek divine guidance. He emerged and decided to take the initiative and launch an attack when his enemy came into range. The religious element of the battle was apparent as Constantine’s men marched under his Christian standard (the Labarum) while Licinius’s troops displayed images of Rome’s pagan gods. Licinius apparently feared the labarum and wouldn’t allow his men to attack it or even look at it directly.
While Constantine often liked to employ clever strategy during his battles, Chrysopolis was different. He decided to launch a huge full frontal assault at the enemy in what was an incredibly successful move. Licinius’ army fell apart and was routed. According to one ancient historian, Zosimus, Licinius lost up to 30,000 men in the battle. He fled and later agreed to surrender, but after a few months in captivity, he was executed while his son was murdered the following year.
Constantine the Great was now the sole ruler of the entire Roman Empire and ensured that Christianity became the empire’s religion by banning pagan sacrifices in 324. Pagan temple treasures were confiscated and used to pay for the creation of Christian churches. He outlawed gladiatorial games and issued harsh punishments for ‘sexual immorality.’ Crucially, Constantine decided to move the empire’s capital from Rome to the site of Byzantium in the eastern part of the empire. He built the city beginning in 324 and consecrated it in 330. Constantinople became one of the greatest cities on earth and thrived while Rome was soon sacked and conquered.