History

Cuicuilco emerged as a significant ceremonial and residential centre in the Valley of Mexico during the Early Pre-Classic period, perhaps as early as 1000 BC. By 400–200 BC it had grown into one of the most important cities in central Mexico, rivalling the early phases of Teotihuacan. Its principal monument was built in four successive construction phases over several centuries, each phase encasing the previous structure in a new shell of compacted earth and volcanic stone; the summit bore a fire altar documented by early excavations. The surrounding city covered several square kilometres, with dense residential zones, craft production, and agricultural terraces on the hillslopes above the valley floor.

The city’s catastrophic end came around 100 AD when the Xitle volcano erupted and produced a lava flow covering approximately 80 square kilometres of the southern Valley of Mexico under lava averaging 10 metres thick. The population fled northward; many are believed to have joined the growing city of Teotihuacan, whose dramatic rise to dominance of the Valley of Mexico coincides almost exactly with Cuicuilco’s destruction. The lava field that buried Cuicuilco — still visible today as the Pedregal de San Angel — preserved the archaeological deposits beneath in an undisturbed state for nearly two millennia.

Systematic excavations began in the 1920s under Manuel Gamio and continued intermittently through the 20th century. The lower stories of the pyramid have been explored by tunnelling through the lava. The full extent of the urban deposit remains largely unexcavated: estimates based on surface survey and sub-lava soundings suggest the buried area is enormous, but access is structurally limited by the hardened lava cap and the presence of UNAM and urban infrastructure directly above the buried city.