Parts of the Amazon previously thought to have been almost uninhabited were actually home to thriving populations of up to a million people, researchers say.
Archaeologists have uncovered evidence of hundreds of villages in the rainforest, away from major rivers, that were home to different communities speaking a variety of languages.
It had been assumed that ancient communities preferred to live near these waterways but new research has found this was not the case.
Researchers say the discovery fills a major gap in the history of the Amazon and provides further evidence that the rainforest has been heavily influenced by those who lived in it.
A team from the University of Exeter found the remains of fortified villages and mysterious earthworks called geoglyphs, man-made ditches with square, circular or hexagonal shapes.
Some of these earthworks show no evidence of being occupied and it is possible that they were used as part of ceremonial rituals.
Dr Jonas Gregorio de Souza, from the University of Exeter's Department of Archaeology, said: "There is a common misconception that the Amazon is an untouched landscape, home to scattered, nomadic communities.
"This is not the case. 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."
Archaeologists uncovered the remains of villages and geoglyphs in the current Brazillian state of Mato Grosso.
They analysed charcoal remains and excavated pottery to establish that a 1,800km stretch of southern Amazonia was continuously occupied from 1250 until 1500 by people living in fortified villages.
The experts estimate that there would have been between 1,000 and 1,5000 enclosed villages and say two-thirds of these sites are yet to be discovered.
Their research estimates that there were 1,300 geoglyphs across 400,000km2 of Southern Amazonia, with 81 found in the area surveyed as part of the study
Villages were often found nearby, or inside the geoglyphs, and were connected through a network of causeways.
Some had been elaborately constructed over many years, the researchers say.
They believe the earthworks were probably made during seasonal droughts, which allowed forests to be cleared.
Drier areas still had fertile soils, where farmers would have been able to grow crops and fruit trees.
Professor Jose Iriarte, also from the University of Exeter, said: "We are so excited to have found such a wealth of evidence.
"Most of the Amazon hasn't been excavated yet, but studies such as ours mean we are gradually piecing together more and more information about the history of the largest rainforest on the planet
"Our research shows we need to re-evaluate the history of the Amazon.
"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."
The research, funded by National Geographic and the European Research Council project PAST, is published in the journal Nature Communications.
It was carried out by academics at the University of Exeter, Federal University of Para, Belem, National Institute for Space Research--INPE and the Universidade do Estado de Mato Grosso.