ometimes called "The Castle" or" The Pyramid of Kukulkan", this structure dominates the center of Chichén Itzá. It’s the most impressive and widely recognized of the structures in Chichén Itzá or indeed anywhere in the Mayan region, and is a true masterpiece of the Toltec-Maya architectural genius.
El Castillo rises 25 meters above the plaza of Chichén Itzá. The base of the pyramid is 55.5 meters on each side. References to the solar calendars of the Toltec and Maya are carefully built into el Castillo. Each of the four stairways has exactly 91 steps, totalling 364, the top platform being number 365, equalling the number of days in the solar calendar. The pyramid has 52 panels in the nine terraces; 52 is the number of years in the Toltec cycle. Each of the nine terraced steps is divided in two: 18 for the months in the yearly Maya calendar. The staircases have balustrades with carved feathered serpents, the open-jawed head at the foot and the rattle held high at the top.
El Castillo represents the Snake Mountain, a mystic place in Mayan folklore believed to be the seat of creation. Snake Mountain is a symbol adopted in Teotihuican as well as the Aztec capital of Tenochtitlan. Though brought to its full artistic maturity at Chichén Itzá, the design is much older than any of these cities. There are examples of the Snake Mountain design at Waxaktun and at Cerros from as early as 100 BCE.
Two upright bodies of the snakes serve as columns for the pyramid's upper temple, which are meant to represent the Kuxan Sum or "living cord" that connected the rulers of the earth with their gods.
During the Spring and Autumn equinoxes, at the rising and setting of the sun, the corner of the structure casts a shadow in the shape of a plumed serpent - Kukulcan, or Quetzalcoatl - along the west side of the north staircase. On these two days, the shadows from the corner tiers slither down the northern side of the pyramid with the sun's movement to the serpent's head at the base.