How did the old Roman religion die out? Was there a major catalyst that increased the spread of Christianity? I am very curious as to what religious life for the average Roman was as Christianity was on the rise. Were people forced to abandon their old beliefs in order to accept the new ones of their dictator? I understand that Constantine I legalized Christianity- but why? How did he become involved in the religion and was it the legalization that caused the rest of the population shift? What happened to the statues and temples to the Roman Gods?
Thanks!
For a comprehensive answer to this question, I highly recommend The Triumph of Christianity by Bart D. Ehrman. He painstakingly makes the case that Christianity went from an obscure Jewish sect with perhaps 40 followers to thirty million in four hundred years; not through miracles, martyrdoms and mass conversions, but by word of mouth and social networks. As if anticipating the disbelief of his reader, he emphasizes that 25% growth per decade can lead to such numbers. It is the original viral-growth killer app. There are a few points worth highlighting.
One, Paul's innovation was to separate belief in Jesus Christ as the son of God and Messiah from the rest of Jewish belief. Circumcision and dietary codes were removed as barriers to adoption
Two, prior to Christianity, the only revealed and exclusionary religion in the western world was Judaism, and Jews weren't interested in proselytizing. Paganism (which is really a Christian ex post facto label for what was just every day spiritual life) was not exclusivist, so an imbalance existed. Christians constantly sought to convert to their exclusive belief system but no countervailing pressure to convert Christians back to pantheism existed. Thus, over time it was more or less inevitable that Christianity would prevail.