Aztec Xiuhpohualli

The xiuhpohualli, the Aztec solar count, divided the year into eighteen months of twenty days each, three hundred sixty days total, closed by five additional days called the nemontemi, considered so unlucky that no rites, no marriages and as little activity as possible were undertaken during them. No surviving source records intercalation ever being applied to correct the resulting drift against the true solar year, a genuine gap in the record rather than a settled absence, since some modern scholars have proposed the Aztecs may have applied some corrective adjustment that left no clear trace in the surviving codices. Each of the eighteen veintenas carried its own major festival dedicated to specific deities: Tlacaxipehualiztli to Xipe Totec in the second month, Toxcatl to Tezcatlipoca in the fifth, Panquetzaliztli to the war god Huitzilopochtli in the fifteenth, so the solar year was structured as an unbroken sequence of state cult observances rather than a neutral grid with festivals scattered across it. Years themselves were named by combining one of four day signs, Reed, Flint, House and Rabbit, with a number one through thirteen, a naming cycle that returned to its starting combination only after fifty two years.

That fifty two year return was the calendar's most consequential moment, because the xiuhpohualli's year count and the two hundred sixty day tonalpohualli it ran alongside both reached their starting point together only once every fifty two years, a combined cycle the Aztecs called the xiuhmolpilli, the "binding of the years." Its close was marked by the Toxiuhmolpilia, the New Fire Ceremony, most famously performed atop the Hill of the Star near Tenochtitlan: household fires across the empire were extinguished in advance, and a new flame kindled on the chest of a sacrificial victim at the ceremony's climax was carried out to relight them, an act understood to guarantee the sun and the world would continue rather than end. The original state cult version of the xiuhpohualli did not survive the Spanish conquest as a functioning civil calendar; the veintena festivals it structured were suppressed along with the priesthood that ran them. It has not vanished from practice, though.

Contemporary Mexica and Danza Azteca revivalist communities, both in Mexico and among Chicano and Indigenous groups in the United States, have reconstructed elements of the xiuhpohualli for ceremonial use today, work that draws on colonial era sources like the Florentine Codex but necessarily differs from the pre-conquest state cult it descends from.