The Aztec calendar stone, Mexica sun stone, Stone of the Sun (Spanish: Piedra del Sol), or Stone of the Five Eras, is a large monolithic sculpture that was excavated in the Zócalo, the main square of Mexico City, on December 17, 1790. It was discovered while Mexico City Cathedral was being repaired.[3] The stone is approximately 12 feet (3.7 m) across and weighs approximately 24 tons.[4]