Saylor.org's Ancient Civilizations of the World/Christianity and the Roman Empire
Constantine and Early Christianity
While many people tend to exaggerate the growth of Christianity before the 4th century, ninety percent of the empire was not Christian, and there is no evidence that Christianity could have continued to grow. It was the support of the emperor Constantine that transformed Christianity into a driving force in the Roman Empire. “Most authorities agree that by 300 CE, between seven and ten percent of the population of the Roman Empire were Christian.” (Freeman, 215)
Constantine became emperor in 306 CE In 312, Constantine led an invasion of Italy and was triumphant. Stories began to emerge that victory was due to the God of the Christians. There was talk of a dream had by Constantine, in which he was told to place a sign of Christ on the shields of his men. Doing this brought him victory. Another conflicting story reports that before the battle, Constantine saw a cross of light in the sky along with the words “By this sign you shall conquer.” “Christ himself then told Constantine to put Christian images on the shields.” (Freeman, 227) Regardless of whether or not there is any truth to these stories, or if he had already planned to associate Christianity with his victory as a way to bring the religion under the state authority, this was the jumpstart that Christianity needed.
In 313 CE, Constantine, along with Licinius, issued an Edict of Toleration. This edict offered Christians an end to persecution, freedom to practice their religion, and restitution of property. The edict did nothing to privilege Christianity above other religious beliefs, but it acknowledged that continued persecution was not productive and that Christians needed to be welcomed fully into society. “This was the high point of religious toleration within the empire.” (Freeman, 227)
Constantine soon relieved the clergy of all civic duties and banned sacrifice. Later, bishops that had already been relieved of civic duties were given control of local patronage and granted legal powers. At the time, there were many different takes on the role of Jesus Christ in relation to God the Father. In order to settle these disputes, Constantine called the bishops together in 325. Along with settling the disputes, Constantine also wanted to consolidate authority of the bishops and to agree on a date for Easter. They met at the imperial residence at Nicea, and passed the Nicene Creed:
We believe in one God, the Father Almighty, maker of all things visible and invisible; and in one Lord Jesus Christ, the Son of God, the only-begotten of his Father, of the substance of the Father, God of God, Light of Light, very God of very God, begotten, not made, being of one substance with the Father. By whom all things were made, both which be in heaven and in earth. Who for us men and for our salvation came down [from heaven] and was incarnate and was made man. He suffered and the third day he rose again, and ascended into heaven. And he shall come again to judge both the quick and the dead. And [we believe] in the Holy Ghost. And whosoever shall say that there was a time when the Son of God was not, or that before he was begotten he was not, or that he was made of things that were not, or that he is of a different substance or essence [from the Father] or that he is a creature, or subject to change or conversion--all that so say, the Catholic and Apostolic Church anathematizes them.
At the Council of Nicea, each area was assigned a metropolitan bishop. There was also an agreement that the date for Easter would be set according to Roman custom, rather than the Asian one, which still tied the feast to the Jewish Passover.
Before his death in 337 CE, Constantine built his first church on imperial land at the Southern edge of Rome, commissioned the Church of the Holy Sepulchre to be built above the presumed tomb of Christ, and built churches over the burials of martyrs, which included St. Peters Basilica.
The Donation of Constantine
The Donation of Constantine (Latin, Donatio Constantini) is a forged Roman imperial decree in which the emperor Constantine I supposedly transferred authority over Rome and the western part of the Roman Empire to the Pope. Composed probably in the 8th century, it was used, especially in the 13th century, in support of claims of political authority by the papacy, especially in regards to control of the Papal States in the center of the Italian peninsula during the Middle Ages. Lorenzo Valla, an Italian Catholic priest and Renaissance humanist, is credited with first exposing the forgery with solid philological arguments in 1439–1440, although the document's authenticity had already been repeatedly contested since 1001. In his Protestant Reformation, Martin Luther used the forged Donation as part of his critique of the Catholic Church.
"Roman Culture: Constantine and Early Christianity" (Wikibooks) http://en.wikibooks.org/wiki/Roman_Culture/Constantine_and_early_Christianity