The Aztec Sun Stone is a monumental basalt disc about 3.6 metres across, nearly a metre thick and close to twenty-five tonnes, carved with a central face ringed by the sign Ollin, the symbols of the previous world-ages, bands of day-signs, and two fire serpents meeting at the base. Popularly the Aztec Calendar Stone, it is better understood as a cosmological and dynastic monument than a working calendar. Buried after the Spanish conquest, it was rediscovered in the Zocalo of Mexico City in December 1790.
The stone's rediscovery in December 1790 came during roadwork and repaving in the Zocalo, the same excavation campaign that also uncovered the colossal statue of Coatlicue, and both finds were made under Spanish colonial administration two and a half centuries after the conquest, a period in which pre-Hispanic religious monuments were, when found, often reburied or treated as curiosities rather than preserved; the Sun Stone instead was set upright against the wall of the Metropolitan Cathedral, where it remained on public display, though partly obscured by whitewash at various points, until it entered the National Museum of Anthropology's collection in the following century. The ongoing dispute over the identity of the central face, Tonatiuh the sun god in the long-standing reading, or alternatively Tlaltecuhtli the earth deity or a hybrid night-sun figure called Yohualtecuhtli, turns partly on the clawed hands flanking the face and on comparison with other Mexica monuments where Tlaltecuhtli is unambiguously shown devouring sacrificial offerings, a comparison that has shifted a meaningful share of specialist opinion away from the older Tonatiuh identification without producing full consensus. The stone's outer rim carries a date glyph read as 13 Reed, associated with the year the Fifth Sun era was believed to have begun.