Once people thought the Amazon was a near-uninhabited rainforest before the Europeans turned up, but researchers say they have found new evidence that it was in fact a hive of human culture and home to millions of people.

A new study has revealed details of 81 sites in the previously uncharted territory of the Amazon’s upper Tapajós Basin, with settlements ranging from small villages just 30m wide to a large site covering 19 hectares.

Researchers say the new discoveries are helping to unpick what the Amazon would have been like before Europeans arrived.

“The idea that the Amazon was a pristine forest, untouched by humans, home to scattered nomadic populations – we already knew that was not true,” said Dr Jonas Gregorio de Souza, first author of the study from the University of Exeter.

“The big debate is how populations were distributed in pre-Columbian times in the Amazon.”

Writing in the journal Nature Communications, de Souza and colleagues explain how the sites were first discovered by satellite imagery of the area, revealed by deforestation. And how they show evidence of human activity in the form of earthworks.

These include ditches enclosing the sites for fortification, sunken roads, and earth platforms on which houses would have stood.

The team checked 24 of the locations with boots on the ground.

“Everything that we identified on satellite imagery that we tested was an archeological site,” said de Souza, adding that the team also came across fragments of ceramics, polished stone axes and a type of fertile dark earth that is an indication of long-term human habitation.

Wood charcoal associated with ceramic fragments from one site was carbon-dated to between 1410 and 1460 AD.

Dates of many of the sites previously discovered in the southern rim of the Amazon show a peak of activity between 1250 and 1500.

The researchers say the buildings themselves would have been made from wood, and the settlements might have been surrounded by wooden walls known as palisades – although no remains of such posts have been found.

De Souza said the results are exciting because the newly discovered settlements were found near small streams, creeks and springs, adding weight to the idea that people were not only concentrated at sites on fertile floodplains on the edge of major rivers, as was long thought.

“The idea was that in the areas that are located further away from the main rivers, populations maybe were actually smaller and they had a negligible impact on the environment,” said de Souza.

“We demonstrated that these regions may have had pretty large populations as well in the past.”

That, the authors write, also chimes with accounts from the 18th century which reported large villages and wide roads in such areas.

Models based on the research suggest that at the time, the southern rim of the Amazon alone could have been home to between 500,000 and one million people.

But, de Souza added, the arrival of Europeans quickly took its toll.

“We know that diseases travelled much faster than people and probably this population was already weakened by diseases brought by Europeans even before the Europeans set foot on the area,” he said.

The research, which was funded by National Geographic and the European Research Council project Past, also highlights that previously discovered earthworks in other regions along the southern rim of the Amazon were not isolated, but part of a stretch of human settlements running along 1,100 miles from east to west.

But evidence including variations in ceramic styles suggest that populations living around the same time in these different regions had different cultures.

“In each one of the regions of the southern Amazon, you find a different local expression of these architectural traditions – so there are different kinds of site layouts and artefacts that are found in each of the regions,” said de Souza.

Further discoveries are likely – models suggest earthworks might be found over a 400,000 square kilometre area with more than 1300 sites – more than 60 per cent of which have yet to be found.

- Guardian