Christianity was given legal status by the Edict of Thessalonica by co-emperors Gratian, Theodosius I and Valentinian II in 380. This edict made the Catholic Church the only legitimate version of Christianity in the empire, turning it into the state religion.
The Catholic Church at that time was a church which subscribed to the Nicene Creed, a particular interpretation of the trinity. It had two branches, the church of the west (Latin Church) and the church of the east (Greek Church). Later these two churches split and came to be called Catholic and Orthodox respectively. The purpose of this edict was to put a ban all other versions and sects of Christianity, which were branded as heretic. The edict was followed by an official persecution of the sects, especially Arian Christianity, which was very popular around the empire.
Two earlier decrees, the Edict of Toleration by Galerius of 311 by emperor Galerius (311 AD) and the edict of Milan by co emperors Constantine I and Licinius (313 BC) decreed the toleration of Christianity. This granted the Christians freedom to worship and the right to live safely (i.e. not be persecuted). These two edicts did not actually legalise Christianity because this religion had never been made illegal and the edicts were not about legal status. They sanctioned a change of policy from persecution to allowing freedom of worship. The Edict of Milan extended this freedom to all religions. There were several religions in the empire.
Constantine I
Constantine.
Christianity did not easily spread through the Roman Empire. See the related question, "How did Christianity spread throughout the Roman Empire?"
The roman empire itself. But disciples like Paul assisted in spreading the gospel.
There was only one Roman Empire. Moreover, the Roman Empire did not study Christianity. An empire cannot study. The Roman Empire was where Christianity spread from Judea (which was a part of the Roman province of Syria). Both Catholic and Orthodox Christianity developed in the Roman Empire. Originally the were called Latin or Western Christianity and Greek or Eastern Christianity respectively. The former was the dominant form of Christianity in the western part of the Roman Empire and the latter was the dominant form of Christianity in the eastern part of this empire. There were also dissident Christian doctrines and sects.
Constantine I
Constantine.
The Edict of Milan legalized Christianity in the Roman Empire.
Christianity did not easily spread through the Roman Empire. See the related question, "How did Christianity spread throughout the Roman Empire?"
1018
St. Paul.
When Constantine converted Christian, then Christianity became a state religion for the Roman Empire.
When Constantine converted Christian, then Christianity became a state religion for the Roman Empire.
Christianity was legalized in 311AD in the Roman empire, but it wasn't until 381AD after much controversy with doctrines and practices that "Nicene Christianity" was ruled as the only legal religion in the Roman empire. This saw the birth the political superpower; the Roman Catholic Church.
There was not one person who spread Christianity throughout the Roman empire. Christianity began its expansion by the efforts of the original apostles and Paul. These men gained followers who in turn gained followers and the movement snowballed.
Constantine legalized the practice of one's own religion in the Empire; specifically, Christianity.
The roman empire itself. But disciples like Paul assisted in spreading the gospel.