Over the course of more than a millennium, the ancient Greeks and Romans put hundreds of millions of animals to death in acts of sacrifice, yet also developed the first vegetarian literature and made animals subject to legal proceedings. This complex situation affected major trends in ancient philosophy, such as Pythagoreanism, and also ancient cosmological concepts. To some degree, philosophy and religious custom clashed with one another, and philosophers and other writers responded by trying to moderate, ignore or avoid this conflict. Missing from the ancient literature is any concept of animal rights. Scholarship on animal sacrifice, much of it fascinated by the subject of sacrificial violence, has given anthropological and zoological explanations for ancient practices, but has not reached a consensus on why sacrifice was widespread, or on how it fitted into ancient paganism as a whole. Recent writing on the rights and status of animals has only begun to influence scholarship.