The Real Aztec Calendar. Aztecs used a sophisticated calendar system for the calculation of ordinary days and religious ceremonies. The aztec calendar, common in much of mesoamerica, was based on a solar cycle of 365 days and a ritual cycle of 260 days;
The aztec calendar consists of 260 days (13 months, each containing 20 days), which determined the life of each mexica (aztec). It weighs approximately 25 tons and is about 12 feet (3.7 metres) in diameter.