Why did Constantine convert to Christianity and make it the official state religion? And why did furious theological debate immediately erupt and become a major factor in public life?
As with his earlier account of the rise of Christianity, in the masterpiece of literature, The Decline and Fall of the Roman Empire, author and historian Edward Gibbon approaches these questions from the perspective of a secular historian.
Constantine’s Conversion to Christianity
It’s not even clear that Constantine ever had a conversion experience, but later writers very much wanted to believe that there was a decisive conversion. They attributed it to a vision that Constantine and his soldiers supposedly witnessed just before a crucial victory in 312.
Eusebius, a bishop and historian who knew Constantine well, reports that when Constantine and his troops were approaching Rome, there appeared in the sky a luminous cross, and a voice was heard to cry out: “In this sign you shall conquer.” Eusebius gives the words in Greek, but in their Latin form—in hoc signo vinces—they became a central feature of Christian tradition. All of the soldiers saw this phenomenon, and they went into battle certain that God was on their side.
Learn more: Constantine and Athanasius
As an historian, Gibbon was skeptical of miracles, and this one is no exception. He tells us, “The real or imaginary cause of so important an event deserves and demands the attention of posterity,” and promises to separate “the historical, the natural, and the marvelous parts of this extraordinary story, which, in the composition of a specious argument, have been artfully confounded in one splendid and brittle mass.” Yet Gibbon is willing, at least, to conclude that Constantine believed he was telling the truth. Whatever he saw—or thought he saw—he probably did feel certain that he had been given a special sign from God....Constantine probably did feel certain that he had been given a special sign from God. Click To Tweet Gibbon notes also that Constantine waited to be baptized until he was on his deathbed, which he thought suspicious. Modern historians tell us, however, that the practice was far from uncommon. People knew that they were likely to go on committing sins after baptism, and they feared that they would endanger their salvation. By getting baptized at the last possible moment, they hoped to guarantee their welcome in Heaven.
Learn More: The Making of Gibbon the Historian
Whatever Constantine’s vision may have been like, historians today tend to doubt, just as Gibbon did, that he experienced an overwhelming conversion in 312. His commitment seems to have evolved only gradually, which is exactly what Gibbon says: “The nicest accuracy is required in tracing the slow and almost imperceptible gradations by which the monarch declared himself the protector, and at length the proselyte, of the Church.”
If Constantine wasn’t a fervent believer from the beginning, why would he install Christianity as the official religion of the Empire? To Gibbon the answer was obvious: A state religion could be a valuable ally for political absolutism. And unlike the old paganism, Christianity taught obedience to authority as a moral duty, together with patient acceptance of suffering in this vale of tears.
Whatever Constantine’s motives may have been, his conversion was truly a turning point in history. The consequence of this change was to drastically alter the relationship of power between church and state. Peter Brown puts it succinctly: “From being a sect ranged against Roman civilization, Christianity became a church prepared to absorb a whole society.”
This transformation didn’t happen all at once; it wasn’t complete until the reign of Theodosius I, 40 years after Constantine. But right from the start, Gibbon notes, bishops enjoyed legal as well as spiritual jurisdiction. There were no fewer than 1,800 bishops in the Empire.