There have always been tales of vast wealthy cities hidden in the Amazon rainforest. Explorers have died trying to find these cities, and the gold they supposedly contained. Conventional wisdom among archeologists was that the soil was too poor for agriculture, which was crucial for supporting large cities. Besides, they hadn't found any. It turns out that when a large civilization is wiped out or moves away, a rainforest will hide what they left. Trees and other vegetation sprout up, animals and floods leave their mark, and before you know it, all that's left are rumors. Oh, these places are still there, you just can't get to them.
Lately, concrete evidence of advanced societies in the Amazon has come to light. Deforestation uncovered some clues. Now a remote-sensing laser system called lidar has detected 26 urban centers hidden by the forest in southeast Bolivia. Two of them each cover an area three time the size of Vatican City! These cities contain pyramids, walls, elevated roadways, terraces, and buildings. The largest site, called Cotoca, belonged to the Casarabe culture, which flourished between 500 CE and 1400 CE. Their disappearance predates European invasion, and scientists don't know what happened to them. Read about the new discoveries at Nature.
Wow? Vatican City is about 0.7 times the National Mall in Washington DC