Amazon rainforest was transformed over 2,000 years ago by mysterious earthworks
Amazonian earthworks such as these are discussed quite a bit in Charles Mann's <i>1491</i>, mostly in the context of dual hypotheses that the Amazon (and much of N. and S. America) was both far more heavily populated, and far more ecologically managed, than previously thought. It's a great and fascinating book, although not as data rich and scholarly as it could be.<p>I don't recall Mann having much description of what the earthworks were used for, although there were suggestions of some of them being fish corrals during high water events, I believe.