The dream of Constantine before the battle of the Milvian Bridge
On 28 October 312 Constantine beat Maxentius at the Milvian Bridge. Lactantius tells of a dream, Eusebius of a cross in the sky: two accounts compared.
Few dreams have had historical consequences comparable to the one that, according to Christian sources, Constantine had on the eve of his clash with Maxentius at the gates of Rome. The battle of the Milvian Bridge, fought on 28 October 312, gave him control of the Roman West and opened the way to the gradual rise of Christianity within the empire. But what really happened that night? The ancient testimonies do not agree, and comparing them is a small laboratory of historical method.
The account of Lactantius
The source closest to the events is Lactantius, a Christian rhetorician who was tutor to Crispus, Constantine's son. In his work On the Deaths of the Persecutors, written a few years after the battle, he states that Constantine was told in a dream to have the heavenly sign of God marked on his soldiers' shields before fighting. The emperor obeyed, having painted a symbol that Lactantius describes as a letter X crossed through and bent over at the top.
Scholars debate whether this was the chi-rho, the first two Greek letters of Christ's name superimposed, or a sign resembling the cross. In any case, in Lactantius' account everything happens in sleep: there is no visible phenomenon in the sky and no army as witness, but a private message addressed to the emperor alone.
The cross of light according to Eusebius
Later, in the Life of Constantine written after the emperor's death in 337, Bishop Eusebius of Caesarea tells a fuller story. He claims to have heard it from Constantine himself, who confirmed it to him on oath. During a march, at midday, the emperor and his soldiers are said to have seen in the sky, above the sun, a cross of light with the words «by this conquer».
The following night Christ is said to have appeared to him in a dream with the same sign, ordering him to make a standard of it to be used in battle. Thus, according to Eusebius, the labarum was born, the banner topped by the monogram of Christ. The Latin formula «in hoc signo vinces», by which the episode is known, is a later rendering of the Greek expression reported by the bishop.
Between propaganda and devotion
Historians observe that the two accounts answer different needs. Lactantius writes in the heat of the moment, in an atmosphere celebrating the end of the persecutions; Eusebius writes years later, when Constantine had become the model of the Christian ruler. The fact that a pagan panegyric of 310 speaks of a vision of Apollo that the emperor had in a sanctuary in Gaul shows that Constantine had long linked his power to divine signs.
Some modern scholars have suggested that a real atmospheric phenomenon, such as a solar halo, lies behind the tradition and was later interpreted in religious terms. Others believe the story grew gradually as the years went by. These remain hypotheses, however, and the question is still open. What is certain is that, after the victory, Constantine openly favoured the Church.
The fact remains that Constantine's dream became one of the most frequently depicted subjects in Christian art. Piero della Francesca painted it in the cycle of the Legend of the True Cross in Arezzo, with the emperor asleep in his tent and the angel descending in the night, in one of the first great night scenes in Italian painting.