The Tonalpohualli,the "day-count" in English, is the 260 day sacred calendar of early Mesoamericans. It is especially associated with the Aztecs. The calendar, is neither solar nor lunar, rather, it is based on two cycles: thirteen day cycle and a second cycle of twenty. A day on the calendar is denoted by a number one through thirteen, and by one of twenty day signs, each dedicated to a different god. Although the solar calendar, the Xiuhpohualli is a distinct calendar, the name of the solar year comes from the day of the Tonalpohualli, that the first day of the solar year falls upon. Mesoamerica is the region extending from central Mexico south to the northwestern border of Costa Rica that gave rise to a group of stratified, culturally related agrarian civilizations spanning an approximately 3,000-year period before the European discovery of the New World by Columbus. ... The word Aztec is usually used as a historical term, although some contemporary Nahuatl speakers would consider themselves Aztecs. ...
This period of 260 days constituted the divinatory or ritual calendar, known as tonalpohualli.
The tonalpohualli was subdivided in various ways; in some manuscripts (known as 'tonalamatl' or 'book of days') each of the twenty 13-day periods, or weeks, is shown separately, together with the figure of a god who was especially associated with the first day, but whose influence was supposed to extend over the whole "week".
In some manuscripts the tonalpohualli is arranged on a different system: in five long horizontal rows of 52 days each.
The symbolism of the tonalpohualli is a prediction of the favourable and unfavourable days of the year, making this divinatory calendar the most important calendar in Aztec life.
Therefore, the concept behind the tonalpohualli is similar to an ancient equivalent of the horoscope section of daily newspapers.
Although the xíhuítl and the tonalpohualli are both interesting and important facets of the Calendar, the Aztec Calendar is probably best-known for its centrally-located figures, which illustrate and prophesize the evolutionary cycle of the Aztec world: when the Aztec world began, how it endured and how it would end.