ABSTRACT
The mesopotamian zone of swamps, of cienagas, in which the extraordinary man-made features are found is blocked off on the north by the Tertiary hill lands of the Sabanas de Bolívar and to the east of the Magdalena by outliers of the Sierra Nevada de Santa Marta. The seasonality of precipitation strongly influences the rhythm of life in northern Colombia, as it must have done for the unknown people who built these ridges. The alluvial morphology of the Mompos Depression is in continuous evolution, evidenced by its countless abandoned channels, natural levees, oxbow lakes, and ciénagas. Much of the Sabanas surface was apparently burned every year, probably for the same reason that stockmen burn it today, to improve pasturage. The forests of the floodplains were being converted into pastures of Para grass or native species. The new evidence from northern Colombia substantially reinforces the growing argument that the pre-Columbian population densities of the American tropical lowlands have been grossly underestimated.
