The rediscovery of Greek literature during the Renaissance and, above all, the novel perfection of Classical sculpture produced a revolution in taste that had far-reaching effects on Christian religious art. The most striking characteristic of Greek religion was the belief in a multiplicity of anthropomorphic deities under one supreme god. Priests simply looked after cults, they did not constitute a clergy, and there were no sacred books.The sole requirements for the Greeks were to believe that the gods existed and to perform ritual and sacrifice, through which the gods received their due. To deny the existence of a deity was to risk reprisals, from the deity or from other mortals. The list of avowed atheists is brief. But if a Greek went through the motions of piety, he risked little, since no attempt was made to enforce orthodoxy, a religious concept almost incomprehensible to the Greeks. The large corpus of myths concerned with gods, heroes, and rituals embodied the worldview of Greek religion and remains its legacy. It should be noted that the myths varied over time and that, within limits, a writer-e.g., a Greek tragedian-could alter a myth by changing not only the role played by the gods in it but also the evaluation of the gods' actions.