Hundreds of circles, squares, and other geometric shapes once hidden by forest hint at a previously unknown ancient society that flourished in the Amazon, a new study says. Satellite images of the upper Amazon Basin taken since 1999 have revealed more than 200 geometric earthworks spanning a distance greater than 155 miles (250 kilometers).
http://news.nationalgeographic.com/news/2010/01/100104-amazon-lost-civilization-circles.html