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).



(Related: "Huge Pre-Stonehenge Complex Found via 'Crop Circles.'")



Now researchers estimate that nearly ten times as many such structures—of unknown purpose—may exist undetected under the Amazon's forest cover.



At least one of the sites has been dated to around A.D. 1283, although others may date as far back as A.D. 200 to 300, said study co-author Denise Schaan, an