Naomi, over at Rage against the Pretty Hate Machine, has an enlightening article on the origins of Christianity. She starts with:
Thus I have heard that the Cult of Jesus began in Palestine, but wherever or however it started isn’t as important as what happened to it when it came to Rome where it met, and whose doctrine it eventually adopted, a rival cult that had existed for more than a thousand years before Jesus was said to have been born, dedicated to the Roman God Mithras.
She then goes on to describe some of the ways that Christianity stole the magic and miracles of Mithras and pasted them onto the story of some two-bit, second-rate preacher. Check out the whole article.