QUITO — A huge ancient city has been found in the Amazon, hidden for thousands of years by lush vegetation.

The discovery changes what we know about the history of people living in the Amazon.

The houses and plazas in the Upano area in eastern Ecuador were connected by an astounding network of roads and canals.

The area lies in the shadow of a volcano that created rich local soils but also may have led to the destruction of the society.

While we knew about cities in the highlands of South America, like Machu Picchu in Peru, it was believed that people only lived nomadically or in tiny settlements in the Amazon.

"This is older than any other site we know in the Amazon. We have a Eurocentric view of civilization, but this shows we have to change our idea about what is culture and civilization," says Prof Stephen Rostain, director of investigation at the National Centre for Scientific Research in France, who led the research.

"It changes the way we see Amazonian cultures. Most people picture small groups, probably naked, living in huts and clearing land - this shows ancient people lived in complicated urban societies," says co-author Antoine Dorison.

The city was built around 2,500 years ago, and people lived there for up to 1,000 years, according to archaeologists.

It is difficult to accurately estimate how many people lived there at any one time, but scientists say it is certainly in the 10,000s if not 100,000s.

The archaeologists combined ground excavations with a survey of a 300 sq km (116 sq mile) area using laser sensors flown on a plane that could identify remains of the city beneath the dense plants and trees.

This LiDAR technology found 6,000 rectangular platforms measuring about 20m (66 ft) by 10m (33 ft) and 2-3m high.

They were arranged in groups of three to six units around a plaza with a central platform.

The scientists believe many were homes, but some were for ceremonial purposes. One complex, at Kilamope, included a 140m (459 ft) by 40m (131 ft) platform.

They were built by cutting into hills and creating a platform of earth on top.

A network of straight roads and paths connected many of the platforms, including one that extended 25km (16 miles).

Dr Dorison said these roads were the most striking part of the research.

"The road network is very sophisticated. It extends over a vast distance, everything is connected. And there are right angles, which is very impressive," he says, explaining that it is much harder to build a straight road than one that fits in with the landscape.

He believes some had a "very powerful meaning", perhaps linked to a ceremony or belief.

The scientists also identified causeways with ditches on either side which they believe were canals that helped manage the abundant water in the region.

There were signs of threats to the cities - some ditches blocked entrances to the settlements, and may be evidence of threats from nearby people.

Researchers first found evidence of a city in the 1970s, but this is the first time a comprehensive survey has been completed, after 25 years of research.

It reveals a large, complex society that appears to be even bigger than the well-known Mayan societies in Mexico and Central America.

"Imagine that you discovered another civilization like the Maya, but with completely different architecture, land use, ceramics," says José Iriarte, a professor of archaeology at University of Exeter, who was not involved in this research.

Some of the findings are "unique" for South America, he explains, pointing to the octagonal and rectangular platforms arranged together.

The societies were clearly well-organized and interconnected, he says, highlighting the long sunken roads between settlements.

Not a huge amount is known about the people who lived there and what their societies were like.

Pits and hearths were found in the platforms, as well as jars, stones to grind plants and burnt seeds.

The Kilamope and Upano people living there probably mostly focused on agriculture. People ate maize and sweet potato, and probably drank "chicha", a type of sweet beer.

Prof Rostain says he was warned against this research at the start of his career because scientists believed no ancient groups had lived in the Amazon.

"But I'm very stubborn, so I did it anyway. Now I must admit I am quite happy to have made such a big discovery," he says.

The next step for the researchers is understanding what lies in an adjoining 300 sq km (116 sq mile) area not yet surveyed. — BBC