Calendar wheel. Drawing, watercolor and ink from Mariano Fernandez Echeverria y Veytia, "HIstoria del origen de las gentes que poblaron la America septentrional." Early nineteeth-century facsimile. The tonalpobualli, or sacred calendar, ruled the life of each Mexica (Aztec) and was consulted on all important occasions well before the early-16th-century Spanish conquest. It was made up of 260 days, or 13 months of 20 days each. The inner portions represent the symbols for the 20 days and the sun, moon, and stars.