Archaeology in the Amazon

More evidence is coming out that the Amazon was densely populated in prehistoric times. Hi-tech mapping is documenting networks of causeways and canals, and complexes of large mounds, in areas still covered with dense jungle:

In a study to be published later this summer, scientists detail an ancient system of monumental public works in a swath of the Amazon in eastern Bolivia. The researchers relied in part on satellite pictures to penetrate the thick jungle, allowing them to inventory vast earthen mounds 25 to 30 feet high and tidy networks of canals and causeways, all built centuries ago.

The sheer volume of dirt that had to be moved to build these structures suggests that the area was densely populated and politically organized, the researchers say. And the neat patterns of mounds, canals and other features on the landscape indicate that the infrastructure was highly planned and well-organized -- not exactly the handiwork of villagers leading a hand-to-mouth existence.