Triangles represent monumental mounds; black dots, ponds; thin black lines, canals; light grey areas, forest; white areas, savannah; and dark grey areas, lakes. Inset top left, the northern side of a savannah is crisscrossed by canals but the southern side is dotted with ponds. Inset bottom right, one savannah (to the east) has been modified by the excavation of a densely packed network of drainage canals, and two other savannahs, to the west, are dotted with ponds; in the former, the network of canals drains into Lake Francia located about 4 km to the north. 690 and 695 indicate the locations of the two farm ponds sampled for this study. Inset top right, boundaries of Amazonia as defined in ref. 43 and the image of World Countries Generalized provided by ESRI under the ArcGIS Pro licence. Scale bar, 5 km. Credit: European Commission JRC.
