The Aztecs used a 260-day ritual calendar, the Tonalpohualli. The Tonalpohualli works in the same way as the Maya tzolk’in, with a number from 1 to 13 attached to 20 cycling day-names. Although the Aztecs used a 365-day calendar to measure the solar cycle, they referenced it less often than the Maya.
In the following image, each quadrant represents a god surrounded by a serpent. The day signs attached to each god and the disks in the body of each serpent mark the days of the 13-day period called the trecena.
Aztec Sun Stone or Calendar Stone
Four ages or four “Suns”
The Aztec Year—and its Months and Days
The Aztec Century
The Aztec Year and the Aztec Month
La clave jeroglífica aplicada a la conquista de México
Aztec Day Names in Nahuatl
Drawing is based on an image in the Borgia Codex.