The crisis of the third century seemed to some emperors, including Diocletian, to be the punishment of the gods. Diocletian increased persecution of Christians, hoping that the gods would restore their blessing on Rome. Yet his persecutions were never very widespread or long-lived, and by the late third century most Romans tolerated Christianity, even if they did not practice it.

Constantine reversed Diocletian’s policy and instead ordered toleration of all religions in the Edict of Milan, issued in 313. He supported the church throughout his reign, expecting in return the support of church officials in maintaining order, and late in his life he was baptized as a Christian. Constantine also freed the clergy from imperial taxation and endowed the building of Christian churches. He allowed others to make gifts to the church as well, decreeing in 321: “Every man, when dying, shall have the right to bequeath as much of his property as he desires to the holy and venerable Catholic Church. And such wills are not to be broken.”4 Constantine also declared Sunday a public holiday, choosing it over the Jewish holy day of Saturday because it fit with his own worship of the sun-god, a practice shared by many Romans. Christians henceforth altered their practices to follow the emperor’s decrees.

Helped in part by its favored position in the empire, Christianity slowly became the leading religion, and emperors after Constantine continued to promote it. In 380 the emperor Theodosius (r. 379–395) made Christianity the official religion of the empire. He allowed the church to establish its own courts and to use its own body of law, called “canon law.” With this he laid the foundation for later growth in church power (see Chapter 8).