https://en.wikipedia.org/wiki/Religious_tolerance
Before Christianity became the state church of the Roman Empire, it encouraged conquered peoples to continue worshipping their own gods. "An important part of Roman propaganda was its invitation to the gods of conquered territories to enjoy the benefits of worship within the imperium."[7] Christians were singled out for persecution because of their own rejection of Roman pantheism and refusal to honor the emperor as a god.[8] There were some other groups that found themselves to be exceptions to Roman tolerance, such as the Druids, the early followers of the cult of Isis, the Bacchanals, the Manichaens and the priests of Cybele, and Temple Judaism was also suppressed.