The tonalamatl is a divinatory almanac

Almanac

An almanac is an annual publication that includes information such as weather forecasts, farmers' planting dates, and tide tables, containing tabular information in a particular field or fields often arranged according to the calendar etc...

 used in central Mexico in the decades, and perhaps centuries, leading up to the Spanish conquest

Spanish conquest of Mexico

The Spanish conquest of the Aztec Empire was one of the most important campaigns in the Spanish colonization of the Americas. The invasion began in February 1519 and was acclaimed victorious on August 13, 1521, by a coalition army of Spanish conquistadors and Tlaxcalan warriors led by Hernán Cortés...

. The word itself is Nahuatl

Nahuatl

Nahuatl is thought to mean "a good, clear sound" This language name has several spellings, among them náhuatl , Naoatl, Nauatl, Nahuatl, Nawatl. In a back formation from the name of the language, the ethnic group of Nahuatl speakers are called Nahua...

 in origin, meaning "pages of days".

The tonalamatl was structured around the sacred 260-day year, the tonalpohualli

Tonalpohualli

The tonalpohualli, a Nahuatl word meaning "count of days", is a 260-day sacred period in use in pre-Columbian Mesoamerica, especially among the Aztecs. This calendrical period is neither solar nor lunar, but rather consists of 20 trecena, or 13-day periods...

. This 260-day year consisted of 20 trecena

Trecena

A trecena is a 13-day period used in pre-Columbian Mesoamerican calendars. The 260-day calendar was divided into 20 trecenas. Trecena is derived from the Spanish chroniclers and translates to 'a group of thirteen' in the same way that a dozen relates to the number twelve...

 of 13 days each. Each page of a tonalamatl represented one trecena, and was adorned with a painting of that trecena's reigning deity and decorated with the 13 day-signs and 13 other glyphs. These day-signs and glyphs were used to cast horoscopes and discern the future.

The best surviving examples of tonalamatl are the Codex Borbonicus

Codex Borbonicus

The Codex Borbonicus is an Aztec codex written by Aztec priests shortly before or after the Spanish conquest of Mexico. The codex is named after the Palais Bourbon in France. It is held at the Bibliothèque de l'Assemblée Nationale in Paris...

 and the Codex Borgia

Codex Borgia

The Codex Borgia is a Mesoamerican ritual and divinatory manuscript. It is generally believed to have been written before the Spanish conquest of Mexico, somewhere within what is now today southern or western Puebla...

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