The calendar system was a very important aspect of the Aztec culture. The arrangement of time governed all-important activities of individual life as well as the scheduling and performance of state-organized events. The Aztecs did not experience time as a succession of uniform movements, stretching monotonously from the indefinite past into the indefinite future. There were two aspects of time Aztec time-counting, each with different functions. The first was the tonalpohualli "counting of the days," a 260-day cycle used for the purpose of divination. This repeating round of days formed a sacred almanac, widely used among Mesoamerican peoples long before the Aztecs. The second division of the calendrical system was a 365-day solar count, known as the xiuhpohualli, "counting of the years," which regulated the recurrent cycle of annual seasonal festivals. These two counts worked simultaneously in operation. They work like two rotating gears, in which the beginning day of the larger 365-day wheel would align with the beginning day of the larger 365-day wheel would align with the beginning day of the smaller 260-day cycle every 52 years. The 52-year cycle is a Mesoamerican "century". The change from one 52-year period into the next was always the occasion of an important religious festival.

The 260 -day count
The 260-day cycle was composed of 20 groups of named and numbered days. Each day received a name, such as rabbit, water, flint knife, alligator, jaguar, and so on. These were visually represented by a hieroglyphic sign of the particular animal or object. The cycle of 20 days intermeshed with a rotating cycle of numbers, 1 to 13, each number denoted by dots. After every complete rotation, each number was engaged with a new day. The 260-day cycle was then divided into 20 "weeks" of 13 days each, called trecenas by the Spaniards. Every trecena began with the number 1 and the day-name which came up in the sequence of rotation. So, each combination was unique within the tonalpohualli cycle, for no day in any one week could be confused with that of another

The 365-day count
The annual ceremonial calendar of the Aztec state was governed according to the 365-day solar count, the xiuhpohualli. This period was divided into 18 "months" of 20 days each, called veintenas by the Spanish, also a 5-day period between the old year and the new. Each veintena had its own special festival, closely correlated to the agricultural year. The years were named after the "year bearer," one of four possible day-names of the tonalpohualli which could begin a new year with its accompanying number, according to the system of rotation. The possible year-names were rabbit, reed, flint knife, and house. The years were distinguished by their numbers. So 1 rabbit, 2 reed, 3 house, 4 flint knife, until 13 numbers and the 4 day and year names began to repeat themselves every 52 years. The succession of 52-year cycles was not calendrically differentiated. Imagine if are centuries were labeled as either before or after Christ. In, the Aztec system, only a knowledge of historical events would allow one to place them in the appropriate 52-year cycle. I was customary in writing, or in sculptured inscriptions, to indicate year-names and their numbers by enclosing them in a square cartouche. The conclusion of a 52-year cycle and the beginning of a new one was the occasion for special ceremonies. At the time the "binding of the years" took place, marked by the ceremonial tying of a bundle of 52 reeds, the xiuhmopilli.