Nero was the first emperor to start persecuting Christians, and many emperors after him did the same. They hoped to destroy Christianity but they only made it stronger.
Constantine was remembered as the first Christian Roman emperor. He made it no longer a crime to be a Christian and made the Edict of Milan.He later made the city of Constantinople.
The Roman Empire fell after being split in half and being invaded by the Germanic Tribes. Rome also had many problems within the empire like the emperor stealing from the treasury and having many rulers in a short period of time.