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"
Months of the Aztec Year
The Aztec Century
The Aztec Year & the Aztec Month
La clave jeroglífica aplicada a la conquista de México
Aztec Day Names in Nahuatl
1519 to 1522 and Aztec equivalents
Drawing is based on an image in the Borgia Codex.