Claim: In Mexico, the winter solstice festival was the most important celebration of the year as it is when, according to the  Aztec calendar, Tonantzin Guadalupe (the mother of the gods) was celebrated.
Evidence: In Mexico, the winter solstice festival was one of the most important celebrations of the year that came on December 12 according to the Julian calendar used by the Spanish until 1582. According to the Aztec calendar, Tonantzin Guadalupe (the mother of the gods) was celebrated on the winter solstice, and she is still feted on December 12, while their most important deity, the sun god Huitzilopochtli, was born during the month of December (panquetzaliztli).