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). The parallel in time between this native celebration and the celebration of Christmas lent itself to an almost-seamless merging of the two holidays. Seeing the opportunity to proselytize, Spanish missionaries brought the reinvented religious pageant to Mexico where they used it to teach the story of Jesus' birth. In 1586, Friar Diego de Soria obtained a Papal bull from Pope Sixtus V, stating that a Christmas mass should be observed throughout Mexico on the nine days preceding Christmas Day.