By Bart D. Ehrman, The University of North Carolina, Chapel Hill
In The Life of Constantine, historian Eusebius writes about the information he received from Constantine himself about his conversion to Christianity. It occurred when Constantine began to reflect on his two imperial colleagues who had tried to overthrow Maxentius and had suffered ignominious defeat. Both were worshippers of pagan gods. Thus, Constantine felt, that the divine assistance, for such an enormous task, would have to come from elsewhere.

The Vision
When it came to divine intervention, in Constantine’s view, obviously, the polytheistic option wasn’t working. And so, according to Eusebius, Constantine decided to rely on one God alone, his father’s. And he was rewarded with a vision. In fact, the vision came to Constantine’s entire army.
At midday, they looked up to the sky and saw a trophy in the shape of a cross with a text attached to it that said ‘By this, conquer’. Constantine had no idea what it meant. But that night he had a dream, in which Christ himself appeared to him and instructed him to make a copy of what he had seen as an object that would allow him to conquer his enemies.
Eusebius says that Constantine still had no idea what this was or what it meant. This shows that he was decidedly not a Christian yet. He called in spiritual advisors who told him that this was the sign of the cross and who explained who Christ was.
The Labarum

Constantine ordered the object to be made: A tall pole plated with gold with a crossbeam making it in the shape of a cross, with a jeweled wreath at the top with two Greek letters super imposed. The letter chi looks like an x and the letter rho, like a capital P. These letters are the first two letters of the name of Christ and this trophy is called the Labarum.
Constantine reportedly carried the labarum into battle against Maxentius and won. He entered Rome the next day as its ruler and as the emperor of the entire western half of the empire. After that, he won every battle he fought with it. Thus, Constantine converted to the worship of Christ because Christ and his God were the most powerful of all.
Lactantius
We also have another account written by a Christian scholar named Lactantius. It was written, in fact, just a few years after the event. This account is intriguing in no small part because Lactantius knew Constantine personally.
Lactantius was a famous rhetorician. And, not long after the emperor’s rise to power, he was appointed to be the personal tutor for Constantine’s eldest son, Crispus. He was then part of Constantine’s household, and obviously had unusual opportunities to hear tales of the emperor’s life.
Lactantius’s account of Constantine’s conversion appears in a booklet that he wrote called Deaths of the Persecutors. In this book, this Christian apologist describes the horrible and excruciating deaths that were suffered by the Roman officials who has been responsible for persecuting Christians.
This article comes directly from content in the video series The Triumph of Christianity. Watch it now, on Wondrium.
Lactantius’s Account of Constantine’s Conversion
Lactantius relates what Constantine apparently had told him, which was that on the night before the Battle at the Milvian Bridge, he had had a dream.
In the dream, an unknown figure told him to have the heavenly sign of God decorated on the shields of his soldiers. And again, similar to Eusebius’s account, it was in the shape of the Chi-Rho. Armed with this sign, they attacked the troops of Maxentius, defeated them, recaptured Rome, and convinced of the power of Christ, Constantine converted.
Differing Accounts
As is obvious, that the accounts differ and so do the explanations of how to resolve the differences. Scholars have devised numerous theories, some of them involving a single dream or vision that Constantine remembered differently over the years. Some of them involving lots of dreams over a long period of time.
One problem is that scholars who study the phenomenon of conversion have shown that committed converts, to a brand-new religion, often tell the story very differently years later based on what has happened in the meantime, which affects the memory of the event.
As a result, we’ll probably never know the precise details. What’s clear is that Constantine started out as pagan, but he became not just a henotheist but a follower of Christ alone.
Unfamiliarity with Christianity
It is likely that the conversion probably took place in stages: The panegyric of 310 CE may be right—Constantine became a henotheist worshiping Sol Invictus, as his father had. And Eusebius and Lactantius may be right—that coming into the battle with Maxentius two years later, Constantine felt a desperate need for divine help. And in his anxiety, he had a dream, or a vision, or both, or more.
Perhaps, it is also likely that Constantine didn’t understand at first and had to get advice and learn more about what his dream vision meant. This shows that he was, clearly, not familiar with the Christian religion.
However, it could also be that he did not stop worshiping Sol Invictus in order to start worshiping Christ. It may be that he finally realized that Sol Invictus was Christ, not Apollo. He had earlier identified him as the pagan god. Now he identified him with Christ.
A Committed Christian?
Buttressed by that realization, and either carrying the labarum or shields decorated with the Chi-Rho or both, his armies attacked the enemy at the Milvian Bridge and won the battle, and Constantine became a committed Christian. Or did he? That’s one of the biggest questions people have posed of Constantine over the years.
Was this a sincere conversion? Did he really commit to Christ or was he a pagan at heart? Or rather, was he a politician at heart who claimed allegiance to Christ only because of the political benefits that he saw could result. Those are the questions that might be that hardest to answer!
Common Questions about How a Vision Led to Constantine’s Conversion
At midday, Constantine’s army looked up to the sky and saw a trophy in the shape of a cross with a text attached to it that said ‘By this, conquer’.
Constantine reportedly carried the labarum into battle against Maxentius and won. After that, he won every battle he fought with it.
Lactantius’s account of Constantine’s conversion appears in a booklet that he wrote called Deaths of the Persecutors.