Originally a pre-Zoroastrian Iranian god, whose Indian equivalent was Mitra, Mithra was a solar deity diminished in stature by the Zoroastrian reforms. He became popular in the Roman Empire in the early centuries of the Common Era as the center of the cult of Mithraism. Like many monomythic heroes, he was said to have been conceived miraculously. Born from a rock, he went on to search for and to slay the primal bull, a symbol of sin and disorder. Mithraism, with its rituals of sacrifice, rivaled early Christianity in Rome.