It is known that Emperor Diocletian who ruled from 302-305 AD adopted a comprehensive anti-Christian approach. All his successors continued the hostilities towards the church and Christians especially in Rome. But soon the Romans realised that such religious intolerance was futile. In around 311 AD Galerius, who was one of the many ruling Caesars, issued an Edict of Toleration after being frustrated. This edict proclaimed religious tolerance for all subjects and saved Christians from execution.
After the death of Galerius, Constantine the Great from the Western Empire seized the opportunity and forged a similar agreement in 313 AD which is known as Edict of Milan. Constantine was supported by Licinus from the Eastern Empire. The edict was more sympathetic towards Christians and reflected Constantine’s liberal views. During this time Christian causes were even funded from the Roman royal treasury. In 323 AD Licinius broke from Constantine’s religious doctrines mentioned in Edict of Milan. And 40 years hence Constantine’s nephew Julian also went against his uncle’s policy of religious tolerance. Julian reinstated the severities that Christianity faced earlier. He took measures to reinstate Greco-Roman religion once again.
There are many doubts over the chronology and development of this Edict of Toleration. But its certain that Christians got back some of their civic rights through this edict. Though some researchers have stated that Constantine made Christianity into official religion of the Roman Empire. But such a synopsis is wrong. Constantine’s edict only prohibited any kind of persecution against the Christians. The Christians were free to practice their religion. There were no further rights given to the Christians through the Edict of Milan.
It was during the reign of Theodosius I that the Roman Empire became more appreciative of Christians. Theodosius I issued the Cunctos Populos in 380 AD which made orthodox teachings on Trinity and Incarnation of Jesus Christ mandatory for all the citizens. If anyone did not take these teachings then he or she was deemed as a mad person. In 381 Theodosius I summoned removed all church leaders who practiced Arianism. He also took steps against Roman officials who participated in the Greco-Roman religious sacrifices. By 392 AD all pagan worship was banned by Theodosius I. Such aggressive religious policies established Christianity as the state religion. From fourth century onwards Christianity was the dominant religion in the Mediterranean area.