Archaeologists have discovered the 'lost valley' of ancient cities in the Amazon rainforest

Archaeologists have discovered a group of lost cities in the Amazon rainforest, which were home to at least 10,000 farmers about 2,000 years ago.

A series of dirt mounds and buried roads in Ecuador were first observed more than two decades ago by archaeologist Steven Rusten. But at the time, “I wasn't sure how it all fit together,” said Rustin, one of the researchers who announced the findings Thursday. In Science magazine.

Modern mapping using laser sensor technology has revealed that these sites are part of a dense network of settlements and connected roads, located in the forested foothills of the Andes, that lasted about 1,000 years.

“It was the lost valley of cities,” said Rostin, who directs investigations at France's National Center for Scientific Research. “It's unbelievable.”

The researchers found that the settlements were occupied by the Obano people between about 500 BC and 300 to 600 AD, a period roughly contemporary with the Roman Empire in Europe.

Residential and ceremonial buildings were located on more than 6,000 earthen mounds surrounded by agricultural fields and drainage canals. The largest roads were 33 feet wide and extended 6 to 12 miles.

Although population numbers are difficult to estimate, the site was home to at least 10,000 people — and perhaps as many as 15,000 or 30,000 at its peak, said archaeologist Antoine Dorison, a co-author of the study at the same French institute. This is similar to the population of London in Roman times, which was then the largest city in Britain.

“This shows very dense occupation and a very complex society,” said University of Florida archaeologist Michael Heckenberger, who was not involved in the study. “For the region, it is in a class of its own in terms of how advanced it is.”

Building roads and thousands of earthen mounds would have required a sophisticated system of organized labor, said José Iriarte, an archaeologist at the University of Exeter.

“The Incas and Mayans built with stone, but people in the Amazon typically didn't have stone available for building — they built with clay,” said Iriarte, who had no role in the research. “There's still a tremendous amount of work to do.”

The Amazon is often viewed as “pure wilderness with only small groups of people. But recent discoveries have shown us how complex the past really was,” he said.

Scientists have also recently found evidence of complex rainforest communities that predated European contact elsewhere in the Amazon, including Bolivia and Brazil.

“There has always been an amazing diversity of people and settlements in the Amazon, and there has never been just one way to live,” Rustin said. “We're just learning more about them.”