Aztec Sun Stone (Piedra del Sol)

Carved in the late post-Classic period and buried in the Zócalo shortly after the conquest, rediscovered in 1790 during drainage repairs, the Sun Stone is the public statement that the world has ended before and will end again. Its concentric rings record the four suns that ended, jaguar, wind, fire-rain, water, and the fifth, the present sun, whose name is the earthquake glyph Ollin in Tonatiuh's mouth at the centre. Around them run the 20 day-signs and the bands of the heavens.

The stone is not a working calendar in the functional sense; it is a cosmogram, a picture of time as a wheel that has already turned four times. The Mexica placed themselves inside the fifth and final sun, the one that moves on a single motion and will close in earthquakes, and the monument is the empire's way of saying so at its heart.

The stone is the built object of the recurring catastrophe. Where most traditions keep the end in story, the Mexica cut it in basalt and set it in the plaza where the people passed every day. The world ages are literal here, engraved and dated by the suns that preceded this one.

Its original placement and purpose remain argued. The leading readings make it either a cuauhxicalli, a vessel for sacrificial hearts, or a temalacatl, the gladiatorial stone to which captured warriors were tied for combat; neither is settled, and the monument may never have stood in public view at all. What is certain is the date of its rediscovery, 17 December 1790, when it was unearthed face-up near the cathedral on the orders of the city authorities, and the decision to mount it on the cathedral wall, where Mexico City residents walked past it for most of a century before it entered the museum.

The face at the centre is not, on the current consensus, the moving sun but Tonatiuh or possibly the earth monster Tlaltecuhtli, and the debate matters because it decides whether the stone speaks about the present sun's death or about the earth that demands feeding. Either way the message runs in the same direction: this world is a term, not a possession.