Traditionally, the archaeologists have the vast Amazon region of South America to be a cultural backwater compared to the better-known civilizations that developed in the Americas. Scholars stress the limitations of tropical environments and lack of critical technological innovations to sustain civilizations. In recent years, the documentation of intensive agriculture, black earth, managed forests, hydraulic engineering, and large settlements has questioned traditional assumptions. Dr. Erickson has documented fascinating monumental earthworks called geoglyphs, ring ditches, or geometric enclosures that cover several acres to nearly a square mile. The geometric patterns suggest a concern for landscape design, high visibility, and aesthetics. Deep ditches imply that huge volumes of earth moved. Various hypotheses are presented for the functions of earthworks. The existence of earthworks of such magnitude and density throughout Western Amazonia shows the ability of native peoples to transform their landscapes at a massive scale.