The tonalpohualli Nahuatl pronunciation: /toːnaɬpoːˈwalːi/, a Nahuatl word meaning "count of days", is a the Aztec version of the 260-day calendar in use in pre-Columbian Mesoamerica. This calendar is neither solar nor lunar, but rather consists of 20 (ventas), 13-day (trecenas) periods. Each trecena is ruled by a different deity.
The basis of the tonalpohualli, is unknown. Several theories have been advanced for this calendrical period: that it represents a Venusian cycle, that it represents the human gestation period, or that it represents the number of days between the zenithal passage of the sun in the tropical lowlands. On the other hand, some scholars including J. E. S. Thompson suggest that the tonalpohualli was not based on natural phenomenon at all, but rather on the integers 13 and 20, both considered important numbers in Mesoamerica.
The other major Aztec calendar, the xiuhpohualli, is a 365 day year, based on 18 months of 20 days and five nameless days. A xiuhpohualli was designated by the name of its first tonalpohualli day. For example, Hernán Cortés met Moctezuma II on the day 8 Wind in the year 1 Reed (or November 9, 1519 in the Julian calendar).
The xiuhpohualli and the tonalpohualli would coincide approximately every 52 years.
In the Aztec calendar, there are twenty day signs.
|Cipactli||Caiman or aquatic monster|
|Ocelotl||Ocelot or Jaguar|
|Ollin||Movement or Earthquake|
|Tecpatl||Flint or Knife|
Gallery of Day Signs
Note that the symbols are arranged counterclockwise around the calendar round.