- from AztecsFor the Aztecs, keeping track of time was key for both religious reasons and for planting crops. They had two separate calendars: a solar calendar and a sacred calendar. The Aztecs divided their history into 52-year time periods, and each 52-year period was a “Sun.” The Aztecs believed they lived in the time of the fifth Sun. The dates on the solar and religious calendars came together once every 52 years. Near the end of each Sun, the Aztecs feared the Sun would set and never rise again. If that happened, their world would end.