Constantine the Great
Constantine was the first Christian Roman emperor. His rule changed the Christian Church greatly. In February 313, Constantine met with Licinius in Milan where they made the Edict of Milan. The edict said that Christians could believe what they wanted. This stopped people from punishing Christians, who had often been martyred, or killed for their faith. It also returned the property which had been taken away from them. In 311, Galerius had made a similar edict, though it did not return any property to them. In pagan Rome before this, it had been against the law to practise Christianity, and Christians had often been tortured or killed.  Constantine protected them.  He went on to organize the whole Christian Church at the First Council of Nicea, even though he himself did not get baptized until near the end of his life.