Mike asked about the Eucharist and its possible relationship to Mithraism. I have to be honest up front and say, I don’t have a lot of information on this question. But I’ll share my thoughts about the alleged connection. If you look at the web you’ll find many sites making claims that Christianity, and especially its practice of the Eucharist, originated in Mithraism. There is no denying the seeming parallels between these two religions, as well as with other Greek and Roman mysteries. Both grew to prominence within Imperial Roman culture at about the same time. It is also quite likely that the December 25th date for Christmas comes from Mithraism – Mithra was apparently born on December 25th from a rock. Ironically Mithraism essentially became the religion of the Empire (Sol Invictus) on the eve of Christianity’s ascendancy in the Roman Empire.
Mithraism was a Roman mystery religion with long roots in Ind-Aryan culture, and most especially in Iran, where it competed with Zoroastrianism. As a Roman religion, it was especially prominent among soldiers and even had a military like structure and initiated only males. Christianity, at least prior to Constantine, wasn’t popular with the military, and if you read closely the New Testament, this was a faith for both women and men.
Although there are parallels, I fail to see any real evidence of direct influence, especially regarding the New Testament descriptions of the Eucharist. Besides, there are sufficient resources within Judaism to explain the Eucharist, which in the New Testament is rooted in the Passover celebration and Jesus’ practice of table fellowship. That the mystery religions created a fertile soil for Christianity’s eventual success, is undeniable. It’s also possible that some later liturgical developments were influenced by a confluence of ideas with Mithraism. But I think you’ll find even greater foundations within Platonic and Aristotelian philosophy – especially regarding the church’s eventual understanding of the real presence.
So, did the Eucharist originate in Mithraism, I find that possibility to be quite unlikely. For, the differences are even greater than the similarities (I don’t think you’ll find any sacrifices of bulls or immersion in the blood of a bull in any of the Christian initiation rites).
Reference: Helmut Koester, Introduction to the New Testament: History, Culture, and Religion of the Hellenistic Age, (Fortress Press, 1982), 1: 372-374.
John Koenig, The Feast of the World's Redemption, (Trinity Press Intl., 2000). [Koenig doesn't say anything about Mithraism, but he does give a historical account of the origins of the Eucharist].