The shortest day of the year, when the Sun reaches its southernmost point. In Aztec cosmology, this was the moment of Huitzilopochtli’s rebirth on Coatepec, his victory over the forces of darkness. At Teotihuacan, the Pyramid of the Sun and the Street of the Dead align with the sunset on this date. The winter solstice was not merely an astronomical marker but a cosmic crisis point: if the rituals failed, if the offerings were insufficient, the Fifth Sun might not return. The Panquetzaliztli festival (originally aligned with this date before calendrical drift) reenacted this annual death and rebirth of the solar god.