A religion that was practiced exclusively by the Roman hierarchy between 200-400 CE. It was the state religion for a short time before Christianity recieved it's backing from Constantine. Mithraism centered around a figure named Mithra who was born from a rock, had twelve disciples, taught Baptism and Eucharist, and was crucified. Like Christianity it had seven central rituals called sacraments. The two main sacraments were Baptism and the Lord's Supper. Ironically, Christianity ended up dominating the empire because it was backed by the Mithraic, Constantine.
Christianity borrowed a lot from Mithraism.