This is the Aztec solar year calendar. It consists of 18 months, with each month equaling 20 days. The last five days of the year were called Nemontemi, the "barren" or empty days and were considered to be unlucky.

The first day of each month was solemn and no work was allowed, much like Sunday used to be in Christian nations. Each day of the month had a name and a corresponding god/goddess to be honored.