A big day in history: “A cross of light” leads Constantine to victory

The clash at the Milvian Bridge on 28 October has gone down as one of history’s decisive battles. If the chroniclers are to be believed, Maxentius had partly destroyed the bridge in readiness for the siege, so his men crossed the Tiber on a hastily assembled pontoon bridge of wooden boats. The emperor drew up his forces, perhaps 75,000 strong, with the river at their backs, but it was Constantine who struck first, sending in his cavalry, who had been so effective for him in the past. As Maxentius’s line buckled, Constantine’s infantry joined the attack, pushing their adversaries back towards the river. Maxentius began to pull his men south, presumably to make a stand on the other side. Sagging under their weight, however, the improvised wooden bridge began to break up. “The boats with the men disappeared in the depths,” wrote Eusebius, “and first that most impious one himself [Maxentius], then the shield-bearers who were with him, sank like lead into the mighty waters, as the divine oracles had foretold.”

Maxentius’s body was not found until the following day, when his severed head was exhibited throughout Rome as proof that he was dead. By this time, Constantine had already entered the city in triumph. Unusually, however, he did not visit the Temple of Jupiter to make the traditional sacrifices – a sign, perhaps, that here was a different kind of emperor. A year later, he issued the Edict of Milan, which, for the first time, made Christianity legal. And in May 337, just days before his death, Constantine was formally baptised, becoming the first Christian emperor in history.

By now, legends were already circulating about Constantine’s victory at the Milvian Bridge, all those years ago. At the time of the battle, the emperor had not formally been a Christian, even though his mother, Helena, had undoubtedly taught him about her faith. For Christian chroniclers, however, it seemed obvious that his victory had been divinely inspired. The historian Lactantius claimed that on the night before the battle, the emperor had had a dream. It told him “to cause the heavenly sign to be delineated on the shields of his soldiers, and so to proceed to battle. He did as he had been commanded, and he marked on their shields the letter X, with a perpendicular line drawn through it and turned round thus at the top, being the cipher of CHRIST.”

Eusebius, however, told a different story, which he claimed to have heard from Constantine’s own lips. On the morning of the battle, he wrote, the future emperor had had a vision. Praying for divine aid, Constantine looked up, and there he saw “a cross of light” blazing in the heavens, and with it, ‘By this sign, conquer’ in Greek.

Can this really have happened? We will never know. Perhaps all that matters, though, is what the story signified. By the end of Constantine’s reign, Christianity was well on the way to becoming the most popular creed in the Roman world. If that battle on 28 October had gone the other way, how different things might have been.

Dominic Sandbrook is a historian and presenter