Cuicuilco, Archaeological site in Tlalpan, Mexico City.

Cuicuilco is an archaeological site in the Tlalpan district of Mexico City, where a large circular pyramid built from stepped stone terraces forms the central structure. The pyramid stands in a broad plain, partly surrounded by hardened lava that once flowed across the area and sealed certain zones.

Cuicuilco began as a farming village around 800 BCE and grew into a regional urban center with an estimated 20,000 inhabitants. Its main pyramidal base was built between 800 and 600 BCE. The Xitle volcano erupted between 245 and 315 CE, burying the city in lava; the population dispersed, and Teotihuacan later became the leading center of the highlands.

The site was restored after its rediscovery, and archaeologists uncovered traces of offerings and ritual objects that remain visible in selected areas today. Visitors can see how this early society held ceremonies in the open air, directly on the pyramid terraces, where people gathered to observe the sky.

The site is mostly open and flat, allowing visitors to view the pyramid from different angles, while a small museum nearby displays finds from excavations. Most paths are easy to walk, and shade is sparse in some areas, so sun protection is advisable.

The pyramid's circular shape differs markedly from the rectangular structures of later Mesoamerican cultures, pointing to distinct building traditions. Parts of the original surface remain preserved beneath the lava layer, helping researchers reconstruct life before the disaster.