Tenochtitlan

The Mexica told of a migration ended by a sign, an eagle on a cactus growing from a rock in the lake, and built their city on that spot. At its centre stood a single pyramid carrying two shrines side by side. The southern one belonged to Huitzilopochtli, the patron who had led them, born fully armed on the hill of Coatepec and killing his sister Coyolxauhqui as she came to attack their mother; the northern one belonged to Tlaloc, the ancient rain god of the highlands, whose side of the platform was painted blue. One structure therefore carried both the tribal war god and the farmer's rain god, and the two halves are usually read as the dry season and the wet, the mountain of war and the mountain of sustenance.

Rebuilt at least seven times, each stage encasing the last, the pyramid preserved its earlier selves inside it. Excavation since 1978, begun when electricity workers struck a carved disc of the dismembered Coyolxauhqui at the foot of the stair, has recovered more than two hundred offering caches: greenstone masks from other regions and older centuries, corals and sawfish rostra from both coasts, jaguars, eagles, a wolf dressed in gold, sacrificial knives with inlaid faces.

Two later finds have changed the picture again. A monolith of the earth deity Tlaltecuhtli, carved face up and weighing many tonnes, was lifted in 2010, and from 2015 archaeologists have exposed part of the great skull rack described by the Spanish, a tower and platform of human crania that the sources said stood before the temple and that had been assumed to be exaggeration.

Two calendars ran at once. The solar year of eighteen months of twenty days, each with its own festival, ended in five days regarded as dangerous and empty. Alongside it ran a count of two hundred and sixty days built from twenty signs and thirteen numbers, which named every person born under it and governed divination. The two counts came back into alignment every fifty two years, and at that turning all fires in the city were put out and a new one was drilled on a hill outside it, carried back by runners to relight the temples and then the households. Failure was understood to mean the end of the present sun.

That is the frame in which Mexica sacrifice has to be read. The Fifth Sun existed because gods had thrown themselves into a fire to create it, and human offering was owed in return; the state made the debt an institution, with schools training the sons of nobles for priesthood and warfare, wars fought to take captives alive, and public rites at which the victims were displayed and dispatched before the city. Scholars disagree sharply about the numbers involved and about how far the practice served politics rather than piety, and the surviving descriptions come mostly from Spanish and mission trained writers with reasons of their own.

The city fell in August 1521 after a siege of some three months, to Cortes with far larger forces from Tlaxcala and other states hostile to the Mexica, and with a smallpox epidemic already through the population. The cathedral of Mexico City was built from the temple's stone, a few steps from where it stood.