Christians had always been subject to local discrimination in the empire, but early emperors were reluctant to issue general laws against the sect. It was not until the 250s, under the reigns of Decius and Valerian, that such laws were passed. Under this legislation, Christians were compelled to sacrifice to pagan gods or face imprisonment and execution. After Gallienus's accession in 260, these laws went into abeyance. Diocletian's assumption of power in 284 did not mark an immediate reversal of imperial inattention to Christianity, but it did herald a gradual shift in official attitudes toward religious minorities. In the first fifteen years of his rule, Diocletian purged the army of Christians, condemned Manicheans to death, and surrounded himself with public opponents of Christianity. Diocletian's preference for activist government, combined with his self-image as a restorer of past Roman glory, forebode the most pervasive persecution in Roman history. In the winter of 302, Galerius urged Diocletian to begin a general persecution of the Christians. Diocletian was wary, and asked the oracle of Apollo for guidance. The oracle's reply was read as an endorsement of Galerius's position, and a general persecution was called on February 24, 303.
Persecutionary policies varied in intensity across the empire. Where Galerius and Diocletian were avid persecutors, Constantius was unenthusiastic. Later persecutionary edicts, including the calls for universal sacrifice, were not applied in his domain. His son, Constantine, on taking the imperial office in 306, restored Christians to full legal equality and returned property confiscated during the persecution. In Italy in 306, the usurper Maxentius ousted Maximian's successor Severus, promising full religious toleration. Galerius ended the persecution in the East in 311, but it was resumed in Egypt, Palestine, and Asia Minor by his successor, Maximinus. Constantine and Licinius, Severus's successor, signed the "Edict of Milan" in 313, which offered more comprehensive acceptance of Christianity than Galerius's edict had provided. Licinius ousted Maximinus in 313, bringing an end to persecution in the East.
The persecution failed to check the rise of the church. By 324, Constantine was sole ruler of the empire, and Christianity had become his favored religion. Although the persecution resulted in the deaths of—according to one modern estimate—3,000 Christians, and the torture, imprisonment, or dislocation of many more, most Christians avoided punishment. The persecution did, however, cause many churches to split between those who had complied with imperial authority (the traditores), and those who had remained "pure". Certain schisms, like those of the Donatists in North Africa and the Meliteans in Egypt, persisted long after the persecutions. The Donatists would not be reconciled to the Catholic Church until after 411. In the centuries that followed, some Christians created a "cult of the martyrs", and exaggerated the barbarousness of the persecutionary era. These accounts were criticized during the Enlightenment and after, most notably by Edward Gibbon. Modern historians have tended to downplay the scale and depth of the Diocletianic persecution.