The geometric ditched enclosures, raised fields, causeways, mounds, and dark fertile soils found across parts of the Amazon basin — physical evidence that the rainforest, long imagined as empty wilderness, was home before 1492 to large and complex human societies that shaped the forest itself, and one of the most debated discoveries in American archaeology.
Cattle ranchers clearing Brazilian rainforest in the 1970s exposed something strange in the bare red earth: enormous ditches cut into perfect squares and circles, hundreds of feet across, laid out by societies whose settlements had been abandoned or transformed long before modern researchers mapped them. Across the wider basin lay raised farm fields, long straight causeways, village mounds, and patches of black soil far richer than the forest around them. For a century, scholars had taught that the Amazon could never feed more than scattered bands. The earth said otherwise. So how many people once lived here, and how much of this forest did they make?