Site where a group of Chichimec, under the leadership of Xólotl, succeeded in gaining power in the Valley of Mexico, establishing their center there in 1224, now the northern suburbs of Mexico City. Its large pyramid is best surviving example of pyramids of Chichimec and Aztec type and it is thought to resemble the Great Temple at Tenochitlán. It was covered at 52-year intervals by at least six successive pyramid and temple buildings. It consists of two parallel stairways leading to two temples on the top of the one structure, with traces of Talud-Tablero style architecture, indicating Teotihuacan occupation in Classic Period. An altar decorated with a skull and crossbones motif is similar to one at Tula.