From time immemorial celestial observation has inspired deeply religious sentiments in man. The sight of an ever-mutable sky and unexpected celestial phenomena gave the impression that the sky was a sublime domain, controlled by the gods. However, to a diligent observer's mind, such a mystifying and unknowable environment represented a powerful incentive to exercise critical thought and attempt to explain what caused these impressive events. Curious observers gradually came to collect information about, and gain an understanding of, the behaviour of the firmament. This made possible the development of calendrical systems that, in turn, dictated the organization of human society.

Mesoamerica as a cultural region developed independently of others for at least three millennia. During this long period there were practices, common beliefs and customs which characterized and defined Mesoamerican culture. One of those cultural aspects was the Mesoamerican calendrical system. Simply put, the system consisted of two simultaneous counts of days. One count was a derivative of the solar year of 365 days organized into eighteen periods of twenty days (veintena) and an additional five days. The other count, of religious origin, had only 260 days organized into twenty periods of thirteen days (trecena). Both counts started simultaneously. After the first 260 days, the counts came out of phase and one had to wait 52 years of 365 days in order to end both counts simultaneously. They then started simultaneously once again.