Chichén Itzá is one of the most important ruins on Mexico's Yucatán Peninsula. It is located about 120 kilometers east of Mérida in the state of Yucatán. Its ruins date back to the late Maya period. With an area of 1,547 hectares[1], Chichén Itzá is one of the most extensive archaeological sites in the Yucatán. The center is occupied by numerous monumental representative buildings with a religious and political background, from which a large, largely preserved step pyramid protrudes. There are ruins of upper class houses in the immediate vicinity. Between the 8th and 11th centuries, this city must have played a nationally important role. However, what this exactly looked like has not yet been clarified. What is unique is how different architectural styles appear side by side in Chichén Itzá. In addition to buildings in a modified Puuc style, there are buildings that have Toltec features. In the past, this was often attributed to a direct influence of emigrants from central Mexico or conquerors from Tula. Today we tend to use diffusionist models and assume that different stylistic forms in monumental buildings are largely simultaneous. The construction of Kukulcán ("El Castillo"), like other Mesoamerican temples, likely reflected the common practice by the Maya of executing several phases of construction for their temples. The last construction probably took place between 900–1000 AD, while the substructure may have been constructed earlier, between 600–800 AD. Based on archaeological research, construction of Kukulcán was based on the concept of axis mundi.[5] Anthropologists think that the site remained sacred regardless of how the structure was positioned on the location. When a temple structure was renewed, the former construction was destroyed using a ritual that involved resolving the space of spiritual forces to preserve its sacredness.[5] It is estimated that this last construction dates to the eleventh century AD. The older, inner temple is referred to as the "substructure". El Castillo (Spanish pronunciation: [el kas'tiʎo], Spanish for "the castle"), also known as the Temple of Kukulcan is a Mesoamerican step-pyramid that dominates the center of the Chichen Itzaarchaeological site in the Mexican state of Yucatán. The temple building is more formally designated by archaeologists as Chichen Itza Structure 5B18. Built by the pre-Columbian Maya civilization sometime between the 8th and 12th centuries AD, the building served as a temple to the deity Kukulcán, the Yucatec Maya Feathered Serpent deityclosely related to Quetzalcoatl, a deity known to the Aztecs and other central Mexican cultures of the Postclassic period. It has a substructure that likely was constructed several centuries earlier for the same purpose. The temple 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. Around the spring and autumn equinoxes, the late afternoon sun strikes off the northwest corner of the temple and casts a series of triangular shadows against the northwest balustrade, creating the illusion of the feathered serpent "crawling" down the temple. To contemporary visitors, the event has been very popular and is witnessed by thousands at the spring equinox, but it is not known whether the phenomenon is a result of a purposeful design since the light-and-shadow effect can be observed without major changes during several weeks near the equinoxes.[1] Scientific research led since 1998 suggests that the temple mimics the chirping sound of the quetzal bird when humans clap their hands around it. The researchers argue that this phenomenon is not accidental, that the builders of this temple felt divinely rewarded by the echoing effect of this structure. Technically, the clapping noise rings out and scatters against the temple's high and narrow limestone steps, producing a chirp-like tone that declines in frequency.[2][3] All four sides of the temple have approximately 91 steps which, when added together and including the temple platform on top as the final "step", may produce a total of 365 steps (the steps on the south side of the temple are eroded). That number is equal to the number of days of the Haab' year and likely is significantly related to rituals.[4] The structure is 24 m (79 ft) high, plus an additional 6 m (20 ft) for the temple at the top. The square base measures 55.3 m (181 ft) across.