For centuries, people thought that the Amazon jungle was uninhabitable. Now, according to David Grann at The New Yorker, scientists have discovered 210 geometric structures on a recently deforested patch of land that could date back to the 3rd century A.D. The structures stretch more than 250 kilometers from northern Bolivia into Brazil. Over the centuries, thousands of explorers died in pursuit of civilization in the Amazon. In his own quest into the Amazon, Grann, who wrote The Lost City of Z, found 20 pre-Columbian settlements built between 800 and 1600 A.D., which included houses, moats, plazas, and walls.