The Aztec (Mexica) Sun Stone is a monumental carved basalt disc, roughly 3.6 metres across and weighing some 24 tonnes, excavated in the main square of Mexico City in 1790 and now in the National Museum of Anthropology. At its centre is a face, most often identified as the sun deity Tonatiuh, though some scholars argue for the earth being Tlaltecuhtli.
Framing the face is the glyph Nahui Ollin, Four Movement, drawn as an X-shaped cross of four broad panels with four dots, which names the present, fifth cosmic age and is read as a warning that this era too, like the four before it, is destined to end in catastrophe, by earthquake. Around it are the four panels naming those four previous world-ages, or Suns, that Mexica cosmology held had each ended in a disaster of its own, water, wind, fire, or the devouring of the first humans by jaguars. Rings of the twenty day-signs of the ritual calendar and of solar rays complete the design, so the same central cross that gives the present age its name also sits at the exact convergence point of the whole calendrical and cosmological scheme carved around it. That day-sign ring runs in the fixed sequence used throughout Mexica timekeeping, opening with Cipactli, the crocodile or earth-monster, and closing with Xochitl, the flower, the same twenty-sign cycle that combined with the numbers one to thirteen to produce the two-hundred-and-sixty-day tonalpohualli used for divination and ritual scheduling, so the stone displays that count permanently even though it was never a device for tracking a specific running date.