Aztec calendar stone, Mexico, Late Postclassic period, c1200-1521. From the Great Pyramid of Tenochtitlan. At the centre is the mask of Tonatiuh. Surrounding this is a group of symbols depicting the earthquake which will end the world. Around this are all the signs of the days of the Aztec year. The next ring represents the rays of the sun and around this are serpents representing the material universe. From the National Museum of Anthropology, Mexico City.