The centerpiece of Chichén Itzá, El Castillo stands 24 meters tall with an additional 6 meters in height for the temple atop the pyramid. Numerous archeological excavations have determined the pyramid was constructed between the 9th and 12th centuries AD and follows a common step pyramid design, with a ground plan of square terraces with stairways up each of the four sides to the temple. Each side contains 91 stairs to the apex which, when summed and including the temple floor at the top, total 365 - equal to the number of days of the Haab' year.