At an excavation of the Great Aztec Temple in Mexico City, amid carvings of skulls and a dismembered warrior goddess, David Carrasco stood before a container filled with the decorated bones of infants and children. It was the site of a massive human sacrifice, and for Carrasco the center of fiercely provocative questions: If ritual violence against humans was a profound necessity for the Aztecs in their capital city, is it central to the construction...