Constantine converted to Christianity. No one denies that. The problem is that we don’t know when and how.
The best-known story is that in October 312, Constantine defeated his rival Maxentius in a battle near the Milvian Bridge, just north of Rome. Prior to the battle, the victor had seen a cross in the sky together with the words “in this sign you will conquer”. After the fight, Constantine put an end to the persecution of the Christians and became a Christian himself. This is, more or less, as we learn it in school, this is how painters like Raphael have shown it, and this is how it is described by Eusebius, in the Life of Constantine (1.26-32), which he wrote in the late 330s.
At the end of his life, Constantine was indeed a Christian. If we cannot accept Eusebius’ statement that the emperor was baptized several days before his death in 337 – and some methodological scepticism is always prudent – we can deduce the emperor’s beliefs from the tomb he had designed: he was to be buried in Constantinople, together with relics of the twelve apostles. In other words, Constantine wanted to be commemorated as equal of the apostles (isapostolos) and as a second Christ – perhaps a bit blasphemous for modern Christian sentiments, but not below the standard of a Roman emperor, who was a dominus et deus.
So, Constantine did convert to Christianity. But the story is far more complex than is commonly assumed.
In the first place, the age of the persecutions was over when Constantine and Maxentius clashed. In the western provinces, where not many Christians were living, the emperors had already put an end to persecuting them several years before. There’s some debate about the exact date, but it must have happened before 312. In the eastern provinces, the emperor Galerius terminated the persecutions in 311, shortly before his death. In a malicious treatise called The Death of the Persecutors, the Christian writer Lactantius suggests that God had sent Galerius an exceptionally painful illness to make him see the error of his policy (§33; cf. 2 Maccabees 9.5).
So, the persecutions were not ended in 312, because they were over already. There was no vision either. That was a thing of the past as well: it happened in 309 or early in 310. At this stage, Constantine believed it was a manifestation of Apollo, whom he had identified as the sun-god. We have several coins from this years, like the one shown to the right, which shows Constantine with the sun-god’s chariot on his shield, and Apollo next to him. After Constantine had captured Rome, he rededicated the Colossus of the Sun, next to the Colosseum; that this monument was dear to him, is suggested by the fact that his triumphal arch was almost next to it.
The oldest description of Constantine’s vision is a speech by an anonymous orator (Panegyrici Latini 7 (6) 21.4-5), who was praising Constantine and the city of Trier, and refers to the emperor’s visit to “the most beautiful temple in the world”. Here, he had seen Apollo and Victory, who had offered him wreaths, promising him a rule of thirty years. We do not know what this vision may have looked like, but the description fits a sun halo like the one shown below. Halos are extremely impressive, and a large one may easily have been read as the Sun offering Constantine a wreath (or wreaths – there can be more than one halo), with three crosses indicating the number XXX.
The evidence that Constantine saw only one cross with a written command to win “in this sign” (ἐν τούτῳ νίκα), is more than a quarter of a century younger. It can be found in Eusebius’ Life of Constantine (1.37-40). Under normal circumstances, we would discard this text, because it is younger and appears to be based upon a misunderstanding of the light vision of 309/310. The most plausible scenario is that Constantine experienced a light vision, which he at first interpreted as a sign of Apollo, but later – after he had conquered the Christian provinces in the east (in 324) – reinterpreted as a Christian miracle.
This becomes even more attractive when we take into account that Eusebius does not know anything about a Christian vision in another book, the History of the Church; in §9.9, he describes the Battle at the Milvian Bridge as the prelude to the Edict of Milan, in which Constantine and his ally Licinius reaffirmed Galerius’ decision that Christianity was acceptable, and even promised some compensation to the Church. This must have been Licinius’ proposal, because he ruled in the eastern provinces and the new faith hardly mattered in the West. Apparently, it was Licinius who introduced the pro-Christian policy.
To sum up: Constantine experienced the Light Vision in 309/310, agreed to Licinius’ pro-Christian policy, pursued this policy himself after he had defeated Licinius, became Christian in the last phase of his reign, and reinterpreted the vision. But if this is so plausible, why is everything attributed to the Battle of the Milvian Bridge?
The answer can be found in Lactantius’ Death of the Persecutors, written immediately after the Edict of Milan. He tells that before his fight with Maxentius, Constantine had a dream, in which he was ordered to put the -sign on the shields of his soldiers. When taken out of context, this confirms the story that Eusebius told a quarter of a century later, about the cross vision. The confirmation appears to be strong, especially because in the Life of Constantine, Eusebius continues his account of the vision with a description of Constantine’s military standard, and in his History of the Church, he mentions that the emperor wanted to be shown with the “salvation-bringing symbol” in his hand.
However, Lactantius does not claim that Constantine converted to Christianity and does not even claim that the symbol was Christian. The same applies to Eusebius’ History of the Church: we read that Constantine wanted to be shown with the symbol in his hand, but it is not stated that Constantine realized that it was a Christian symbol. This may seem an unfair objection, but it must be stressed that Lactantius also mentions that Licinius has had a dream, in which angels announced his victory. Because this dream is an obvious invention by Lactantius, it is certainly possible that Constantine’s dream is an invention too.
There’s another problem. The -sign certainly was a Christian symbol in the final years of Constantine’s reign. The symbol was also in use prior to the fourth century: readers used it to indicate in the margin of a text that something was chrestos, “useful”. Because an /e/ and an /i/ were more or less interchangeable at this time (iotacism), it is easy to understand why Christians started to use this well-known sign. The problem is when they started to use this.
There is, to the best of my knowledge, only one -sign that possibly dates to the period before the Edict of Milan. It was found in the Preconstantine necropolis underneath the basilica of Saint Peter’s in Rome. It is certainly possible that this graffito was created by one of the construction workers, building the now famous church. (BTW: after 326, evidence again that Constantine did not pursue an active pro-Christian policy prior to the conquest of the eastern provinces.) To the best of my knowledge, all other -signs postdate the Edict of Milan, which creates the question what was meant by Constantine when he ordered his soldiers to paint it on their shields, why he put it on a standard, and why he wanted to be shown with the “salvation-bringing symbol”.
The answer is that we don’t know for sure, but the symbol happens to be known from a temple of the Sun God from Illyricum. It is a combination of two symbols: the sun ✲ and the moon crescent Ͻ. We do not know whether Constantine knew this, but it is certainly tempting to assume that he had dedicated his army to the god of light, which he first believed to be Apollo, and later believed to be Christ.
I am not claiming to know exactly what happened, but the normal story about Constantine converting after a cross vision and putting an end to the persecutions, is simply not true. It seems that three emperors contributed to the victory of Christianity: Galerius put an end to the persecutions, Licinius started to cooperate with the Church, and Constantine continued this policy, and really converted at the end of his life. He had, literally, seen the light.
There was an interesting response to this article, which is discussed here.