The mysterious lost city, which was uncovered in eastern Ecuador, was built around 2,500 years ago.
Scientists who excavated the area claim that hundreds of thousands of people could have lived there at any one time.
The indigenous Upano people are thought to have built the site which was connected by an intricate network of roads and canals.
Prof Stephen Rostain, director of investigation at the National Centre for Scientific Research in France, who led the research, said it dispels traditional notions of Amazonians.
Historically, archaeologists wrongly believed that the Amazon rainforest was an inhospitable place, sparsely populated by bands of hunter-gatherers who lived as nomads or in huts.
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Archaeologist José Iriarte of the University of Exeter said the discovery “is completely unprecedented in Amazonia and in Andean prehistory”.
Professor Rostain, writing in Science, said: “This is older than any other site we know in the Amazon.
“We have a Eurocentric view of civilisation, but this shows we have to change our idea about what is culture and civilisation.”
The city is more than 1000 years older than any other known complex Amazonian society.
Co-researcher Antoine Dorison added: “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.”
The city was discovered using a laser mapping technology called LiDAR which allows scientists to see through forest cover and reconstruct ancient sites.
The technology found over 6,000 rectangular platforms used to build homes and ceremonial buildings.
One single road was found to stretch 25km (16 miles).
Dr Dorison said: “The road network is very sophisticated. It extends over a vast distance, everything is connected.
“And there are right angles, which is very impressive.”
The researchers claim that the society is even bigger than Mayan societies in Mexico and Central America.
However, little is known about the people who built the city and lived there for 1,000 years.
