Chichén Itzá, El Castillo, west side

Chichen Itza ("at the mouth of the well of the Itza") was a large pre-Columbian city built by the Maya people of the Terminal Classic. The archaeological site is located in the municipality of Tinum, in the Mexican state of Yucatán.

Chichen Itza was a major focal point in the Northern Maya Lowlands from the Late Classic (c. AD 600–900) through the Terminal Classic (c. AD 800–900) and into the early portion of the Postclassic period (c. AD 900–1200). The site exhibits a multitude of architectural styles, reminiscent of styles seen in central Mexico and of the Puuc and Chenes styles of the Northern Maya lowlands. The presence of central Mexican styles was once thought to have been representative of direct migration or even conquest from central Mexico, but most contemporary interpretations view the presence of these non-Maya styles more as the result of cultural diffusion.

Chichen Itza was one of the largest Maya cities and it was likely to have been one of the mythical great cities, or Tollans, referred to in later Mesoamerican literature. The city may have had the most diverse population in the Maya world, a factor that could have contributed to the variety of architectural styles at the site.

El Castillo (Spanish for "the castle"), also known as the Temple of Kukulcan, is a Mesoamerican step-pyramid that dominates the center of the Chichen Itza archaeological site in the Mexican state of Yucatán. The building is more formally designated by archaeologists as Chichen Itza Structure 5B18.

Built by the pre-Columbian Maya civilization sometime between the 9th and 12th centuries CE, El Castillo served as a temple to the god Kukulkan, the Yucatec Maya Feathered Serpent deity closely related to the god Quetzalcoatl known to the Aztecs and other central Mexican cultures of the Postclassic period.

The pyramid consists of a series of square terraces with stairways up each of the four sides to the temple on top. Sculptures of plumed serpents run down the sides of the northern balustrade. During the spring and autumn equinoxes, the late afternoon sun strikes off the northwest corner of the pyramid and casts a series of triangular shadows against the northwest balustrade, creating the illusion of a feathered serpent "crawling" down the pyramid. Each of the pyramid's four sides has 91 steps which, when added together and including the temple platform on top as the final "step", produces a total of 365 steps (which is equal to the number of days of the Haab' year).

The structure is 24 m high, plus an additional 6 m for the temple. The square base measures 55.3 m across.