Porfirio Díaz standing next to the Aztec Sun Stone. 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. The stone is approximately 12 feet across and weighs approximately 24 tons. Ancient Mysteries, Ancient Times, World History, Mexico City Cathedral, Aztec Calendar