350–353 Late period The Battle of the Milvian Bridge took place between the Roman Emperors Constantine I and Maxentius on 28 October AD 312.

Constantine won the battle and started on the path that led him to end the Tetrarchy and become the sole ruler of the Roman Empire.

This was interpreted as a promise of victory if the sign of the Chi Rho, the first two letters of Christ's name in Greek, was painted on the soldiers' shields.

In Rome, the favorite was Maxentius, the son of Constantius' imperial colleague Maximian, who seized the title of emperor on 28 October 306.

But whereas Constantine's claim was recognized by Galerius, ruler of the Eastern provinces and the senior emperor in the Empire, Maxentius was treated as a usurper.

[6] He easily overran northern Italy, winning two major battles: the first near Turin, the second at Verona, where the praetorian prefect Ruricius Pompeianus, Maxentius' most senior general, was killed.

[7] It is commonly understood that on the evening of 27 October with the armies preparing for battle, Constantine had a vision which led him to fight under the protection of the Christian God.

Lactantius states that, on the night before the battle, Constantine was commanded in a dream to "delineate the heavenly sign on the shields of his soldiers" (On the Deaths of the Persecutors 44.5).

According to this version, Constantine with his army was marching (Eusebius does not specify the actual location of the event, but it was clearly not in the camp at Rome), when he looked up to the sun and saw a cross of light above it, and with it the Greek words " Ἐν Τούτῳ Νίκα", En toutōi níka, usually translated into Latin as "in hoc signo vinces".

Eusebius then continues to describe the labarum, the military standard used by Constantine in his later wars against Licinius, showing the Chi-Rho sign.

[9] The accounts of the two contemporary authors, though not entirely consistent, have been merged into a popular notion of Constantine seeing the Chi-Rho sign on the evening before the battle.

Had it done so, it is unthinkable that there should not be a single reference to it in any of the contemporary histories until the Life of Constantine",[16] and that Eusebius's "specific statement that 'the whole army ... witnessed the miracle'"[16] is implausible.

It was expected that Maxentius would remain within Rome and endure a siege; he had successfully employed this strategy twice before, during the invasions of Severus and Galerius.

Ancient sources commenting on these events attribute this decision either to divine intervention (Lactantius and Eusebius, both of whom were Christians) or superstition (Zosimus, who was a pagan).

Additionally, Maxentius is reported to have consulted the oracular Sibylline Books, which stated that "on October 28 an enemy of the Romans would perish".

Maxentius' Praetorian Guard, who had originally acclaimed him emperor, seem to have made a stubborn stand on the northern bank of the river; "in despair of pardon they covered with their bodies the place which they had chosen for combat.

The descriptions of Constantine's entry into Rome omit mention of him ending his procession at the temple of Capitoline Jupiter, where sacrifice was usually offered.

[28] He chose to honour the Senatorial Curia with a visit,[29] where he promised to restore its ancestral privileges and give it a secure role in his reformed government: there would be no revenge against Maxentius' supporters.

"[30] The following year, 313, Constantine and Licinius issued the Edict of Milan, which made Christianity an officially recognised and tolerated religion in the Roman Empire.