Before Teotihuacan, there was Cuicuilco, a Late Pre-Classic site at the southern end of Lake Texcoco. Founded around 1100 - 700 BCE, Cuicuilco, which means "place of prayer" or the "place of the rainbow" in Nahuatl, may be the oldest civilization in the basin of Mexico.

Cuicuilco was originally a farming village. Early large-scale construction in the form of adobe and stone-faced platforms took place around 600-200 BCE, when it grew into a prominent urban area based around a large ceremonial centre, including a large 20 meter high circular stepped pyramid. The urban area includes plazas, avenues, terraces, various buildings and fortifications, and a quite sophisticated irrigation system. Population at the city's peak is estimated at 20,000 people, and its likely the city may have had contact with the Olmec civilization to the south. By 300 BCE the extended community dominated the valley.

Cuicuilco was abandoned following eruptions of the nearby Xitle volcano, which buried the site in lava. Dates suggested for this range from to 50 BCE - 150 CE. There may have been a number of partial-abandonments with the territory being subsequently reoccupied until the site was covered by volcano lava flows up to 10 meters deep that forced total abandonment. Many archaeologists believe that refugees from the volcanic destruction of Cuicuilco migrated north and added to the growth of the six small towns that developed into Teotihuacan.