A trecena is a 13-day period used in pre-Columbian Mesoamerican calendars. The 260-day Mayan 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. It is associated with the Aztecs, but is called different names in the calendars of the Maya, Zapotec, Mixtec, and others of the region.