The calendrical systems devised and used by the pre-Columbian cultures of Mesoamerica, primarily a 260-day year, were used in religious observances and social rituals, such as divination.
Stelae 12 and 13 from Monte Albán, provisionally dated to 500-400 BCE, showing what is thought to be one of the earliest calendric representations in Mesoamerica.
The back of Stela C from Tres Zapotes, an Olmec archaeological site. This is the second oldest Long Count date yet discovered. The numerals 7.16.6.16.18 translate to September 1, 32 BCE (Gregorian). The glyphs surrounding the date are what is thought to be one of the few surviving examples of Epi-Olmec script.
Image of a colonial era Mexican calendar
The Mesoamerican Long Count calendar is a non-repeating base-20 and base-18 calendar used by pre-Columbian Mesoamerican cultures, most notably the Maya. For this reason, it is often known as the Maya
Mesoamerican calendars
…observance of this Calendar Round sequence was of ritual significance to a number of Mesoamerican cultures. A third major calendar form known as the Long Count is found in the inscriptions of several Mesoamerican cultures, most famously those of the Maya civilization who developed it to its fullest extent…
Detail showing columns of glyphs from a portion of the 2nd century CE La Mojarra Stela 1. The left column gives a Long Count date of 8.5.16.9.7, or 156 CE. The other columns visible are glyphs from the Epi-Olmec script.