Aztec sun stone, Monumental sculpture at National Museum of Anthropology, Mexico.

The Aztec sun stone is a circular olivine basalt slab 3.6 meters in diameter and 98 centimeters thick, weighing about 24,590 kilograms. Its rough grey-brown surface carries concentric rings of low-relief carving: a central face with wide eyes and open mouth, eight wedge-shaped points, and an outer band of small square compartments each holding a distinct figure. Two serpents encircle the lower border.

The stone was carved during the reign of Moctezuma II, between 1502 and 1520, as indicated by his name glyph in the central disc. After the conquest it was buried in the Zócalo on the orders of Archbishop Alonso de Montúfar. It was rediscovered on 17 December 1790 during repairs on the Mexico City Cathedral and later moved to the National Museum of Anthropology in 1964.

The stone's modern name, Aztec Calendar, was given by Antonio de León y Gama after its 1790 rediscovery, though the carving itself records Mexica calendrical cycles: 20-day months, 18-month years and 52-year periods. Visitors can pick out the central face and the ring of small square compartments holding distinct figures.

The sculpture stands upright in the Mexica Hall on the ground floor, where you can view it from several angles. Fewer visitors gather in this room during the morning, which allows for a quieter experience.

The central face was disfigured by bullets fired at the stone when United States Army soldiers occupied the Zócalo during the Mexican–American War, though English sources note no evidence of such damage. General Winfield Scott considered taking it to Washington as a war trophy.