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.