Eighteen Twenty Day Months and Five Days Nobody Wanted

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.