Edict of Milan in the context of "Lactantius"

Constantine I (27 February 272 – 22 May 337), also known as Constantine the Great, or known mononymously as Constantine, was Roman emperor from AD 306 to 337 and the first Roman emperor to convert to Christianity. He played a pivotal role in elevating the status of Christianity in Rome, the Edict of Milan decriminalising Christian practice and ceasing Christian persecution. This was a turning point in the Christianisation of the Roman Empire. He founded the city of Constantinople (now Istanbul) and made it the capital of the Empire, which it remained for over a millennium.

Born in Naissus, a city located in the province of Moesia Superior (now Niš, Serbia), Constantine was the son of Flavius Constantius, a Roman army officer from Moesia Superior, who would become one of the four emperors of the Tetrarchy. His mother, Helena, was a woman of low birth, probably from Bithynia. Later canonised as a saint, she is credited for the conversion of her son in some traditions, though others believe that Constantine converted her. He served with distinction under emperors Diocletian and Galerius. He began his career by campaigning in the eastern provinces against the Persians, before being recalled to the west in AD 305 to fight with his father in the province of Britannia. After his father's death in 306, Constantine was proclaimed as augustus (emperor) by his army at Eboracum (York, England). He eventually emerged victorious in Civil wars of the Tetrarchy against the emperors Maxentius and Licinius to become the sole ruler of the Roman Empire by 324.

Early Christians were heavily persecuted throughout the Roman Empire until the 3rd century. Although Christianity initially emerged as a small Jewish movement in 1st-century Judaea, it quickly branched off as a separate religion and began spreading across the various Roman territories at a pace that put it at odds with the well-established Roman imperial cult, to which it stood in opposition; Christians were vocal in their expressions of abhorrence towards the beliefs and practices of Roman paganism, such as deifying and making ritual sacrifices to the Roman emperor or partaking in other methods of idolatry. Consequently, the Roman state and other members of civic society routinely punished Christians for treason, various rumoured crimes, illegal assembly, and for introducing an alien cult that drove many Roman people to apostasy in favour of Jesus Christ. According to Tacitus, the first wave of organized persecution occurred under Nero (r. 54–68), who blamed Christians for the Great Fire of Rome in 64. A number of mostly localized persecutions occurred during the reign of Marcus Aurelius (r. 161–180). After a lull, persecution resumed under Decius (r. 249–251) and Trebonianus Gallus (r. 251–253). The Decian persecution was particularly extensive, as Decius strived to restore the Roman golden age in part by forcing pagan practices upon the Christian community. Another wave of persecution began under Valerian (r. 253–260), but ceased abruptly after he was captured and taken prisoner by the Sasanian Empire during the Battle of Edessa of the Roman–Persian Wars. Under his successor Gallienus (r. 253–268), whose reign was marred by rapidly escalating military conflicts of the Crisis of the Third Century, the first ever decree of tolerance was issued for Christian practices and places of worship, although it stopped short of recognizing Christianity as a religion with legal status.

Emperor Diocletian (r. 283–305) began the Diocletianic persecution, which was the final and the most severe wave of persecution of Christians by the Roman state. It was enforced until the accession of Galerius (r. 305–311), who issued the Edict of Serdica, and the death of Maximinus Daza (r. 310–313). After Constantine the Great (r. 306–337) defeated his rival Maxentius (r. 306–312) at the Battle of the Milvian Bridge in October 312, he and his co-emperor Licinius issued the Edict of Milan, which decriminalized Christianity and suppressed pagan populations throughout the Roman Empire. In 380, Theodosius I (r. 379–395) issued the Edict of Thessalonica, officially establishing Christianity as the Roman state religion. It was also during the reign of Theodosius I that pagan practices were overtly deemed punishable offenses, which laid the framework for early Byzantine anti-pagan policies.

Valerius Licinianus Licinius (/lɪˈsɪniəs/; Greek: Λικίνιος; c. 265 – 325) was Roman emperor from 308 to 324. For most of his reign, he was the colleague and rival of Constantine I, with whom he co-authored the Edict of Milan that granted official toleration to Christians in the Roman Empire. He was finally defeated at the Battle of Chrysopolis (AD 324), and was later executed on the orders of Constantine.

The history of Christianity begins with Jesus, an itinerant Jewish preacher and teacher, who was crucified in Jerusalem c. AD 30–33. His followers proclaimed that he was the incarnation of God and had risen from the dead. In the two millennia since, Christianity has spread across the world, becoming the world's largest religion with over two billion adherents worldwide.

Initially, Christianity was a mostly urban grassroots movement. Its religious text was written in the first century. A formal church government developed, and it grew to over a million adherents by the third century. Constantine the Great issued the Edict of Milan legalizing it in 315. Christian art, architecture, and literature blossomed during the fourth century, but competing theological doctrines led to divisions. The Nicene Creed of 325, the Nestorian schism, the Church of the East and Oriental Orthodoxy resulted. While the Western Roman Empire ended in 476, its successor states and its eastern compatriot—the Byzantine Empire—remained Christian.

The persecution of Christians can be traced from the first century of the Christian era to the present day. Christian missionaries and converts to Christianity have both been targeted for persecution, sometimes to the point of being martyred for their faith, ever since the emergence of Christianity.

Early Christians were persecuted at the hands of both Jews, from whose religion Christianity arose, and the Romans who controlled many of the early centers of Christianity in the Roman Empire. Since the emergence of Christian states in Late Antiquity, Christians have also been persecuted by other Christians due to differences in doctrine which have been declared heretical. Early in the fourth century, the empire's official persecutions were ended by the Edict of Serdica in 311 and the practice of Christianity legalized by the Edict of Milan in 312. By the year 380, Christians had begun to persecute each other. The schisms of late antiquity and the Middle Ages – including the Rome–Constantinople schisms and the many Christological controversies – together with the later Protestant Reformation provoked severe conflicts between Christian denominations. During these conflicts, members of the various denominations frequently persecuted each other and engaged in sectarian violence.

A great martyr (also spelled greatmartyr or great-martyr) or megalomartyr (from Byzantine Greek μεγαλομάρτυς, megalomártus, from μέγας, mégas 'great' + μάρτυς, mártus 'martyr'; Church Slavonic: великомꙋ́ченикъ; Romanian: mare mucenic; Georgian: დიდმოწამე) is a classification of saints who are venerated in the Eastern Orthodox Church and those Eastern Catholic Churches which follow the Rite of Constantinople. The term is also used in Malta especially by parishes dedicated to Saint George in reference to him (San Ġorġ Megalomartri).

Generally speaking, a greatmartyr is a martyr who has undergone excruciating tortures—often performing miracles and converting unbelievers to Christianity in the process—and who has attained widespread veneration throughout the Church. These saints are often from the first centuries of the Church, before the Edict of Milan. This term is normally not applied to saints who could be better described as hieromartyrs (martyred clergy) or protomartyrs (the first martyr in a given region).

The Edict of Serdica, also called Edict of Toleration by Galerius, was issued in 311 in Serdica (now Sofia, Bulgaria) by Roman Emperor Galerius. It officially ended the Diocletianic Persecution of Christianity in the Eastern Roman Empire.

The Edict implicitly granted Christianity the status of religio licita, a worship that was recognized and accepted by the Roman Empire. It was the first edict legalizing Christianity and preceded the Edict of Milan by two years.

The Diocletianic or Great Persecution was the last and most severe persecution of Christians in the Roman Empire. In 303, the emperors Diocletian, Maximian, Galerius, and Constantius issued a series of edicts rescinding Christians' legal rights and demanding that they comply with traditional religious practices. Later edicts targeted the clergy and demanded universal sacrifice, ordering all inhabitants to sacrifice to the Roman gods (Jews were exempt). The persecution varied in intensity across the empire—weakest in Gaul and Britain, where only the first edict was applied, and strongest in the Eastern provinces. Persecutory laws were nullified by different emperors (Galerius with the Edict of Serdica in 311) at different times, but Constantine and Licinius' Edict of Milan in 313 has traditionally marked the end of the persecution.

Christians had been subject to intermittent local discrimination in the empire, but emperors prior to Diocletian were reluctant to issue general laws against the religious group. In the 250s, under the reigns of Decius and Valerian, Roman subjects including Christians were compelled to sacrifice to Roman gods or face imprisonment and execution, but there is no evidence that these edicts were specifically intended to attack Christianity. 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, foreboded 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 at Didyma for guidance. The oracle's reply was read as an endorsement of Galerius's position, and a general persecution was called on 23 February 303.