The Amazon was not always the wild forest we know today. Between approximately 600 BC and AD 850, a civilisation known as Aquiry profoundly reshaped the south-western Amazon basin. Its inhabitants dug immense earthworks forming geometric patterns, linked by straight roads whose remains can still be seen in places today.

A new study, published in Nature, nevertheless reveals that this society was probably far more extensive than previously thought. By combining data from aerial LiDAR surveys with archaeological discoveries already known, researchers estimate that the Aquiry may have constructed as many as 30,000 earthworks across an area of up to 183,000 km². Its population is thought to have peaked at between 1.2 and 3 million inhabitants around AD 200.

For archaeologist and anthropologist Martti Pärssinen of the University of Helsinki, this discovery has profoundly changed his perception of the Amazon. After flying over the first geoglyphs in the early 2000s, he says he recently realised that these structures could be up to ten times more numerous than he had imagined.

LiDAR reveals hundreds of invisible structures

If this civilization remained largely unknown for so long, it is because the forest gradually reclaimed the land after its disappearance, around AD 850. LiDAR surveys have revealed geometric earthworks that had remained invisible because the majority of the constructions are now hidden beneath the Amazonian canopy.

To locate them, researchers used LiDAR, a technology that sends laser pulses from an aircraft. Some of these beams pass through gaps in the vegetation, reach the ground and then return to the sensor, making it possible to reconstruct the terrain without clearing the forest.

The scientists thus mapped nearly 4,500 km² by flying over several long transects in the Brazilian state of Acre. The result: 432 earthworks were recorded, 396 of which had never previously been identified. According to Martti Pärssinen, such a concentration in an area representing less than 3% of Greater Amazonia suggests that many other regions may still contain similar remains.

An Amazon shaped by human beings

These findings challenge a long-standing assumption: that the Amazon remained largely untouched until modern times. Instead, the researchers describe a landscape alternating between forests, inhabited clearings, cultivated land and large ceremonial spaces.

At the heart of these clearings probably stood the immense geometric earthworks, surrounded by long wooden houses accommodating large communities. The inhabitants cultivated maize, cassava, squash and cotton, among other crops, while the surrounding forests were enriched with carefully tended fruit and nut trees. The roads connecting the different sites would also have encouraged exchanges and gatherings, where ceremonies, festivals and community events were held.

Despite this major advance, one mystery remains. Researchers still do not know why this civilisation, which flourished for nearly 1,500 years, disappeared between AD 850 and 1000. It is a question that future explorations of the Amazon rainforest may perhaps help to answer.

See, Personne ne s’attendait à une telle ampleur : l’Amazonie révèle les traces d’une immense civilisation cachée sous sa canopée

Photo. This aerial view reveals a tiny portion of the thousands of earthworks that may still be hidden beneath the Amazon rainforest. © Martti Pärssinen