South of Constantine’s camp, Maxentius was also surrounded by priests. But unlike those in his enemy’s camp, they were pagan priests, and, unlike the Christians, they certainly had the emperor’s full attention. On 27 October 312, the day before the two sides would join battle, Maxentius was in a panic. He was so anxious about whether he had sufficient support from the Roman people to be assured of victory that he turned to his priests and asked them to read the omens. He desperately needed his confidence to be shored up; only a sign from Rome’s traditional gods could do that. The priests cut open the belly of a young animal, delved their hands into its carcass and fingered the intestines. The news was not good.
The augury, so the story goes, indicated that the enemy of Rome would be defeated.18 The atmosphere in the temple was strained. It is reasonable to imagine that a senator or courtier in the assembled group, desperate to avert a complete collapse in the emperor’s morale, tactfully broke the ice. Surely Constantine was the enemy of Rome. Surely he would be the one to fall. That, at least, was the way Maxentius chose to interpret the priests’ announcement. The imperial court breathed a sigh of relief. Indeed, they had reason to feel confident about their prospects. In addition to their superior number of soldiers, they had devised a cunning plan to scupper Constantine’s attack on the city.
To take Rome from the north, Constantine and his army would have to cross the Tiber at Milvian Bridge. (A reconstructed version of this bridge, called the Ponto Milvia, today marks the spot where the original once stood.) Maxentius and his military advisers now made this the central plank of their defence of the city. Maxentius ordered part of the bridge to be destroyed so that the enemy could not cross easily. Alongside it, however, he ordered a temporary floating bridge to be constructed. Crucially, it was made of two parts fastened in the middle by removable iron pins. Maxentius’s forces would come out along this bridge and face Constantine. However, should Constantine’s army force Maxentius back into the city, the defenders of Rome would be able to cross back over the river and then rely on a devastating counter-attack: they would quickly unfasten the pins, watch the makeshift bridge slide apart and thus prevent Constantine from pursuing them. From the Rome-side banks of the Tiber, Maxentius and his advisers believed, they would watch the enemies of Rome fall like lemmings into the river.19
As potentially brilliant as this secret weapon was, Constantine and his army were about to gain their very own psychological advantage. That advantage would spectacularly transform the chances of the outnumbered, anxious Constantine. It would go down in history as one of the most pivotal moments in history, but also one of the most controversial.
Some time before battle was joined, Constantine had a vision. According to Eusebius, at midday, under a bright blue sky, the general saw a shining cross, and inscribed upon it, an instruction: ‘By this sign, you will conquer!’ Another account elaborates: Christ himself appeared with the cross and the order to be victorious was sung by angels.20
Modern historians, suspicious of the fact that Eusebius described the extraordinary moment in great detail in his Life of Constantine, but failed even to mention it in his Church History, have suggested more rational explanations. Perhaps the vision was a natural astronomical event that produced a ‘halo phenomenon’; perhaps Constantine saw a meteor (there is evidence that one landed in this region of Italy at this time). Exactly what he saw, however, is perhaps less important than how he interpreted it. Desperately seeking an explanation, Constantine turned to the Christian priests in his entourage. Whoever was present, be it Bishop Ossius or Lactantius, they now saw an opportunity and seized it with both hands. This, they said, was a sign from God. It was a sign that He was divinely choosing Constantine to defeat the tyrant Maxentius.21
According to Eusebius, Constantine now became convinced that they were speaking the truth. Perhaps he was simply ready and willing to convert. For all his military achievements of the past, he knew he was now facing the most daunting battle of his life. He was leading his soldiers against a vastly superior force and bidding to take the one city that no foreign invader, not even Hannibal, had yet conquered. He needed to put his trust in somebody or something. He needed to know that in return for his devotion there was a god protecting him and his army. Apollo and the monotheistic cult of the Unconquerable Sun had once performed that role: two years earlier Constantine had had another vision in a sanctuary of Apollo in Gaul or Britain.22 Accordingly, after 310 Constantine had his coins stamped with Sol Invictus. But now that pagan deity was being replaced in his thinking by God. For after his spiritual experience before the battle, when he turned to his advisers, he found that this experience was most plausibly explained by the Christians. Constantine was won over.
The Christian priests must not have been able to believe their extraordinary luck. By being in the company of someone who was leaning towards a religious conversion, they had been in the right place at the right time. At last they were not only being listened to by an emperor of Rome, but also obeyed by him.
Constantine wasted no time. Just before battle he made a radical, last-minute change of plan. He ordered all the soldiers to mark their shields in white paint with a sign made up of two Greek letters, chi-rho (XP), the cipher of Jesus Christ. (According to Lactantius, writing four years after the event, Constantine had been given this instruction in a dream before the battle.) Although some of the men would have been Christians, it is likely that the majority were not, so there must have been shock that their commander was asking them to follow him in abandoning the traditional gods. Indeed, at the critical moment before war, when their fears were at their greatest and their superstitions most pronounced, their leader’s command must have induced even more terror. It is possible that Constantine went as far as ordering the metalsmiths in his army to adjust the old Roman standards. Even the defining, talismanic symbol of the pagan Roman army was perhaps adapted to signify the cross.23 The general was determined to take the greatest gamble of his life: to fight the battle under the sign and protection of God.
On 28 October 312 the forces of Constantine and Maxentius collided on a broad plain in front of Milvian Bridge. Maxentius had originally decided to remain in the city, but, buoyed up by his priests’ good augury, he too crossed the Tiber over the provisional wooden bridge along with his men. His fragile morale was immediately challenged, however, when he noticed numerous owls landing on the walls of the city.24 That omen was a fitting symbol of the events that followed. The broad, spacious plain favoured Constantine’s cavalry. Sweeping up along the flanks of the enemy, they threw Maxentius’s army into utter confusion. The fact was that its commitment to fighting for Maxentius had never been resolute. Those soldiers who did put up a fight were trampled underfoot by horses or routed by the following infantry. Slowly but surely, the army of Constantine forced the defenders of Rome back against the Tiber.
With a sudden, collective failure of heart, Maxentius’s troops turned and fled, their general running away faster than any of them. At least, the men perhaps consoled themselves, they could reach their makeshift bridge and make the city their bolt-hole. But Maxentius and his generals had wildly misjudged the effectiveness of their plan B. The temporary bridge could not take the weight of the stampeding survivors from his massive army, and the engineers in charge of unfastening the bolts panicked. Whether spurred by fear or sheer incompetence, they released the metal fastenings too early.