The stepped pyramids, temples, columned arcades, and other stone structures of Chichén Itzá were sacred to the Maya and a sophisticated urban center of their empire from A.D. 750 to 1200. The most recognizable structure is the Temple of Kukulkan, also known as El Castillo. This glorious step pyramid demonstrates the accuracy and importance of Maya astronomy—and the heavy influence of the Toltecs, who invaded around 1000 and precipitated a merger of the two cultural traditions.
The temple has 365 steps—one for each day of the year. Each of the temple’s four sides has 91 steps, and the top platform makes the 365th. Devising a 365-day calendar was just one feat of Maya science. Incredibly, twice a year on the spring and autumn equinoxes, a shadow falls on the pyramid in the shape of a serpent. As the sun sets, this shadowy snake descends the steps to eventually join a stone serpent head at the base of the great staircase up the pyramid’s side.