Mesoamerican calendars

non-repeating base-20 and base-18 calendar used by several pre-Columbian Mesoamerican cultures, including the Maya

one method of determining the date

right|400px|thumb|The original page 13 of the Codex Borbonicus, showing the 13th trecena of the Aztec sacred calendar. This 13th trecena was under the auspices of the goddess [[Tlazolteotl, who is shown on the upper left wearing a flayed skin, giving birth to Cinteotl. The 13 day-signs of this trecena, starting with 1 Earthquake, 2 Flint/Knife, 3 Rain, etc., are shown on the bottom row and the column along the right side.]]

set of nine gods in Mesoamerican mythology

The xiuhpōhualli (, from (“year”) + (“count”)) is a 365-day calendar used by the Aztecs and other pre-Columbian Nahua peoples in central Mexico. It is composed of eighteen 20-day "months," which through Spanish usage came to be known as (“scores, groups of twenty”), with an inauspicious, separate 5-day period at the end of the year called the . The name given to the 20-day periods in pre-Columbian times is unknown, and though the Nahuatl word for moon or month, , is sometimes used today to describe them, the sixteenth-century missionary and ethnographer, Diego Durán explained that:

Aztec mythology belief