By and Large, it didn't. Christianity was swallowed up in the trappings, ritual, and symbolism of the pagan mystery religions in Rome. For example, we know that before the Church merged with the Roman state, the "Pontifex Maximus" was the high priest of the pagans religion in Rome, and the enemy of Christianity. (the early church father Tertullian mentions that in 230 A.D.). However, 200 years later, when the merge happened, the Pontifex Maximus is the official title of the Pope, the head of the Roman Catholic church. Just one of the many smoking guns.
It wasn't until after the enlightenment, with the Reformation, that the Christianity, as it was with the apostles, began to be restored.
