How did the 260-day ritual calendar work in Mesoamerica?

The 260-day ritual calendar, known as the tonalpohualli among the Aztecs and the Tzolkin among the Maya, functioned as a sacred almanac used throughout ancient Mesoamerican cultures for divination and ritual scheduling.123

The calendar operated through the simultaneous meshing of two distinct cycles:
* Numerals: A cycle of numbers from 1 to 13.123
* Day Names: A sequence of 20 unique day names (such as Wind, Jaguar, or Reed).123

Because these cycles ran concurrently, each combination of a number and a name occurred only once every 260 days ($13\times 20=260$).1

Specialized priests, known as tonalpouhque, interpreted these combinations to determine the "fateful character" of each day. Because each day and 13-day period was associated with specific deities, the calendar was used to guide significant life events, including births, marriages, and the election of rulers. For example, individuals born on specific days were believed to have predetermined destinies, such as becoming a drunkard or dying in ritual sacrifice. This system dominated both public and private life, serving as a primary tool for navigating the spiritual and practical challenges of the ancient world.243