or Earthquake Tecpatl Flint or Knife Quiahuitl Rain Xochitl Flower A  trecena  is a 13-day period used in  pre-Columbian   Mesoamerican calendars . The 260-day  calendar  (the  tonalpohualli ) was divided into 20 trecenas. Trecena is derived from the Spanish chroniclers and translates to 'a group of thirteen' in the same