Did Constantine really convert to Christianity, or was it politics?

Nobody can say for certain, and modern historians have argued about it since Jacob Burckhardt in 1853. The facts are these. Constantine ruled the Roman Empire from AD 306 to 337 and is called the first Roman emperor to convert to Christianity. He lived much of his life as a pagan, began to favour Christianity in 312, and was baptised only at the end, by an Arian bishop. In February 313 he and Licinius developed the Edict of Milan, which let Christians follow their faith without oppression and returned confiscated Church property.

The conversion has two famous origin stories that do not match. According to Lactantius, Constantine was directed in a dream to put the heavenly sign on his soldiers' shields before battle, and marked them with the cipher of Christ. Eusebius describes instead a vision at midday of a cross of light above the sun, with the words In hoc signo vinces.

Then the picture gets mixed. The edict protected all religions, not only Christianity. A triumphal arch of 315 shows the goddess Victoria and no Christian symbols, though the Senate, not the emperor, commissioned it. Yet he also backed the Church: he built basilicas, exempted clergy from certain taxes and promoted Christians to high office. He decreed in 321 that Sunday should be a day of rest, and he waited until his deathbed to be baptised, reportedly so that baptism would release him of sins committed in carrying out his policies.

So the question divides scholars. A 19th-century view, from Jacob Burckhardt, saw a scheming secularist, a politician manipulating everyone to secure his own power. Timothy Barnes, in 1981, saw a radical convert on a personal crusade. Arguments continue over the strength and depth of his conversion.