According to Mary Boyce, Mithraism was a potent enemy for Christianity in the West, though she is sceptical about its hold in the East. Filippo Coarelli (1979) has tabulated forty actual or possible Mithraea and estimated that Rome would have had "not less than 680–690" mithraea. Lewis M. Hopfe states that more than 400 Mithraic sites have been found. These sites are spread all over the Roman empire from places as far as Dura Europos in the east, and England in the west. He, too, says that Mithraism may have been a rival of Christianity. David Ulansey thinks Renan's statement "somewhat exaggerated", but does consider Mithraism "one of Christianity's major competitors in the Roman Empire". Ulansey sees the study of Mithraism as important for understanding "the cultural matrix out of which the Christian religion came to birth".