Researchers have revealed the massive scale of "lost cities" in the Amazon rainforest and uncovered new details about the lives of the people who lived there.
The existence of centuries-old settlements constructed by the Casarabe tribe who lived in what is now Bolivia was already well known.
But the extent of the sites had not previously been realised, and details of how the tribe lived was shrouded in mystery.
The veil has been lifted thanks to an aerial survey using technology known as Lidar, which uses a pulse from a laser to collect measurements as well as creating maps and 3-D models.
The existence of around half of the 26 sites surveyed from the air was already known but the rest were new discoveries.
Researchers were stunned by the scale of the settlements, which included pyramids.
The survey also uncovered a surprising level of sophisticated urbanisation including a road network and reservoirs, indicating that the Casarabe were more than hunter-gatherers.
The research suggests that explorers hunting for El Dorado may not have been wasting their time as they hacked their way through the forest with machetes. It was a search which cost British adventurer Colonel Percy Fawcett, 57, his life when he ventured into the rainforest in 1925, never to return.
But Lidar has enabled scientists to strip away the trees and see what lies below.
They examined six different areas. The smallest was four square miles and the largest 32.
Flying in a helicopter 650ft above the Bolivian Amazon, researchers were able to “digitally deforest” the area and find vast urban settlements that were abandoned 600 years ago.
Landivar and Cotoca were known to exist but little was known about them.
Researchers found evidence of canals, roads radiating out from an urban centre, 66ft high pyramids and terraces.
Ceremonial buildings and defensive fortifications were also suggested including a moat and ramparts.
They were inhabited by the Casarabe, a tribe that lived in the Llanos de Mojos region of the Amazon basin between 500 and 1400 AD.
Much less is known about the Casarabe, who used mud for construction, rather than the Maya, who built with limestone.
The discovery of major cities and the satellite settlements has confounded the belief that the Amazon was scarcely populated when Europeans arrived.
Sites that merit exploration
“It’s a myth that was created by Europeans who really spoke of a jungle, and vast regions untouched by humans,” Heiko Prümers of the German Archaeological Institute and one of the authors of the study told Smithsonian magazine.
“So, a lot of people didn’t want to see that there were archaeological sites here that merit exploration.
“I’m sure that in the next 10 or 20 years we’ll see a lot of these cities, and some even bigger than the ones we are presenting in our paper.”
Earlier archaeological research suggested the Casarabe hunted, fished and farmed staples including maize.
The latest findings go some way towards indicating how the settlements were knitted together and their relationship with the cities.
Why the Casarabe disappeared from the region is a matter of conjecture, with any oral history having been wiped out by contact with Europeans and smallpox.
The discovery of reservoirs has led Mr Prümers to suggest they could have been driven away by water shortages.
"Of course, we don’t know if these were for a drinking water supply or to farm fish or turtles, but it’s very interesting that we do have them,” he said.
“We know that there were severe droughts in the Amazon regions several times in history. That might have happened to this culture as well. It only needs one or two years of loss of crops of harvest and people have to move.”