Cuicuilco Circular Pyramid

19.3015°N, 99.1816°W.

The Cuicuilco Circular Pyramid stands in the southern reaches of modern Mexico City, in the Tlalpan borough at the foot of the Ajusco volcanic range. Built between approximately 800 and 200 BCE during the Late Formative, it is one of the oldest pyramids in central Mexico and the only known major circular pyramid from this period. The structure rises 23 metres in five tiered platforms of stacked stone and packed earth, with an original diameter of about 110 metres. The eruption of the Xitle volcano around 50 BCE buried the entire site in lava up to ten metres thick, ending Cuicuilco's existence as a city and accelerating the rise of Teotihuacan to the north. Excavations by Manuel Gamio in 1922 and Byron Cummings in the late 1920s exposed the upper terraces.

The Cuicuilco Pyramid is a building killed by a volcano and preserved by the same lava that ended it.