Keeping track of time was essential to the Aztecs—both for religious reasons and for the planting of crops.
They had two separate calendars, a solar calendar and a sacred calendar, and they divided their history into 52-year time periods. Each 52-year period was a “Sun,” and 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.