The remains of hundreds of villages have been uncovered by archaeologists in the Brazilian rainforest.
Experts have assumed ancient communities preferred to live near waterways, but the recently discovered ruins were located away from major rivers in the area.
“Our research shows we need to re-evaluate the history of the Amazon,” said Professor José Iriarte, from the University of Exeter’s Department of Archaeology, whose archaeologists made the discovery.
“It certainly wasn’t an area populated only near the banks of large rivers, and the people who lived there did change the landscape. The area we surveyed had a population of at least tens of thousands.”
Archaeologists uncovered the remains in the current Brazillian state of Mato Grosso.
A 1120 mile (1,800km) stretch of southern Amazonia was continuously occupied from 1250 until 1500 by people living in fortified villages, the experts found. They estimate that there would have been between 1,000 and 1,500 enclosed villages.
Two-thirds of these sites are yet to be found, meaning the number of people who called that patch of the rainforest could be closer to one million.
Evidence suggests the uncovered villages were home to different communities speaking various languages who had a lasting impact on the environment around them.
Huge parts of the Amazon are still unexplored by archaeologists, particularly areas away from major rivers.
The discovery fills a major gap in the history of the region.
It suggests the theory that the Amazon was once untouched by human farming or occupation is wrong. The new evidence, the archaeologists say, suggests it has been heavily influenced by those who lived in it.
“There is a common misconception that the Amazon is an untouched landscape, home to scattered, nomadic communities. This is not the case,” said Dr Jonas Gregorio de Souza, another member of the research team.
“We have found that some populations away from the major rivers are much larger than previously thought, and these people had an impact on the environment which we can still find today.
“The Amazon is crucial to regulating the Earth’s climate, and knowing more about its history will help everyone make informed decisions about how it should be cared for in the future.”