Christianity
Christianity originally began as a sect of Judaism. It started to move further and further away until, at the destruction of the Jewish Temple and the following revolt, it split and became a separate religion. Christianity, despite being condemned by the pagan followers of the roman gods, began to spread. It spread all over roman society, and although it was usually the religion of the poor farmer it had many upper class followers. It also gained many literate followers who established a religion that could not be stopped by controversy or persecution.
Persecution
Christians were often persecuted for a number of reasons. Many were killed because the pagans thought that they deserved to die for not being pagan. Many of the roman leaders were scared that the Christian leaders would become more important than them. In 64AD the emperor Nero blamed the Christians for the fire that destroyed much of Rome. Some were torn apart by dogs, others burnt alive as human torches. Pagans murdered Christians because the Christians would not sacrifice to their gods and the Pagans worried this would bring the gods wrath on them.
Constantine
Constantine was the turning point for Christianity in Rome. Constantine was a brilliant military leader and rose through the ranks to General. Eventually he became emperor of west Rome and then east Rome. Supposedly he became Christian after he had a vision. The night before a great battle Jesus and his Christian mother Helena cam to him. He said that if they granted him victory he would convert to Christianity. He won the battle and fulfilled his promise. When he became Christian the whole empire became Christian. Suddenly the prosecuted became the powerful. The Pagan temples were replaced with churches. Constantine replaced traditional pagan leaders with Christian leaders. This was the start of the Christian Roman Empire. The Roman church would eventually follow.