Modern and past Indigenous peoples, anthropologists, and even centuries-old missionaries have long known about many of the ritual and symbolic aspects of the complex calendar system of the Aztecs, also known as the Mexica.
This calendar system involved interweaving a solar and ritual calendar; the normal solar calendar had 365 days, while the ritual calendar had 260 days and was divided into 13 groups of 20 days. (Each of these days represented a unique combination of 13-day and 20-day associations and had its own name, symbol, patron deity, and an assignation of either good or evil.)
But the way they calibrated their solar year has long been a mystery. In fact, until recently, scholars had yet to even decipher why the Aztec New Year began when it did — Feb. 23 on the Gregorian calendar, which is used today by Western cultures.
“That was a conundrum for us,” says Exequiel Ezcurra, an ecologist at the University of California, Riverside and the lead author of a study published in PNAS that aimed to find the answer.
