The Cuicuilco pyramid was one of the first true urban centres in the Basin of Mexico. Its construction started a few centuries BC, during the Late Preclassic period. The pyramid is partially covered by a basaltic lava flow produced by the Xitle monogenetic volcano. New stratigraphic work around the pyramid and the volcano together with new radiocarbon dates indicate that the pyramid and nearby settlements were abandoned as a direct consequence of the volcanic activity of Xitle. The new dates, obtained from material which clearly is contemporaneous with the volcanic activity, suggest that the eruption took place around 1670 years BP, some 300 years later than previously thought.