Photo credit, Martti Pärssinen & Fabio de Novaes
Researchers have discovered hundreds of earthworks hidden beneath the canopy of the Brazilian Amazon rainforest, built by an ancient civilization believed to have numbered millions of individuals.
These enormous structures dug into the ground — called geoglyphs — were built thousands of years ago in a region far from major rivers.
“These people were creating monumental geometry in the Amazon at the same time that Pythagoras was developing his theorem in Greece,” explains paleontologist Alceu Ranzi, president of the Institute of Amazonian Geoglyphs and a member of the team.
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Analyze the past
This research, recently published in the journal Nature, was carried out by a team of scientists from universities and institutes in Spain, Finland, Brazil and Denmark.
They scanned the dense forest canopy using a technology called LiDAR (Light Detection and Ranging), which uses laser pulses to measure distances and create complex 3D maps. This makes it possible to analyze large areas without clearing brush or physically going to the site.
Photo credit, Martti Pärssinen
“This was the first truly ambitious LiDAR study carried out in the Amazon,” says Martti Pärssinen, archaeologist, anthropologist and study co-author, from the University of Helsinki.
The team explored an area of 4,400 km². She identified 432 geoglyphs, the vast majority of which had never been recorded, dating from the period from 600 BC. BC to 850 AD AD
Researchers estimate that the so-called Aquiry civilization, at the origin of these constructions, occupied an area of approximately 183,000 km², approximately the size of Cambodia or Syria. It would have had up to three million inhabitants at its peak, between 100 and 300 AD. AD
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Ranzi says the team discovered ditches up to 15m wide and 5m deep. Such imposing structures bear witness to the existence of vast communities working together.
“There are no stones in this region. They probably used wooden tools and baskets to transport the earth,” he suggests.
But the Amazon's humid climate means organic matter decomposes quickly, making it difficult to be certain.
In addition to requiring considerable labor and division of labor, researchers believe that these constructions required extensive knowledge of mathematics and geometry.
What were they used for?
Geoglyphs were once thought to serve as forts or defensive structures, protecting people from invasion.
Photo credit, Rhuan Lopes
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But today, experts believe they more likely served ceremonial and political functions – places of gathering rather than permanently occupied spaces.
“If this is confirmed… then these people should live in peace. The fact that they put so much effort and work into [these geoglyphs] suggests that they had no threatening enemies,” Ranzi speculates.
Pärssinen highlights another conclusion about the survey: a deep respect for nature.
“They never transformed the rainforest into savannah,” he says. “The clearings and felling of trees appear to have been necessary only to maintain their way of life, the cultivation of corn, squash and cassava, and nothing more. »
Excavations indicate that the structures were carefully maintained.
“It wasn't just about building them, but about preserving them for centuries, which obviously required a body of accumulated knowledge,” says another co-author, Rhuan Carlos Lopes, an archaeologist and anthropologist at the Federal University of Pará, Brazil.
Photo credit, Martti Pärssinen, Risto Kalliola & Fabio de Novaes
According to Ranzi, the geoglyphs were not isolated constructions hidden in the forest, but were well connected together.
“We mapped 350 km of roads connecting the geoglyphs,” he explains. “These routes led to the sites, and the roads widened as they approached the structures. »
The end of the investigation
During their research, the researchers noticed something curious: the construction of geoglyphs seems to have stopped around the year 850. It is not known why.
Ranzi draws a parallel with the Mayan civilization, whose main centers in parts of Mexico and Central America were abandoned around the same time.
“The Mayans stopped building and using their palaces. The pyramids of Yucatán have been reclaimed by the forest,” he notes.
“Something similar happened in the Amazon. The 9th century may have been a period of wider environmental crisis. »
Regardless, emerging research, including this study, challenges long-held beliefs that the Amazon rainforest was a wilderness untouched by human occupation.
Over the past decades, studies across multiple disciplines have shown that millions of people lived here long before Europeans arrived and left lasting marks on the structure and composition of the world's largest rainforest.
“What we see in the Amazon is not a vast natural forest, but rather a vast historical garden shaped by human activity,” says Lopes.
Estimates of the region's precolonial population have continued to increase. Previous studies suggested that the entire Amazon could have been home to between one and 2.5 million people, while more recent estimates put the figure at between five and ten million.
If a relatively small area could accommodate up to three million inhabitants, these figures might have to be revised upwards.
Another previous hypothesis was that Amazonian populations lived primarily along large rivers, where food resources were more readily available.
However, geoglyphs are mainly located in mountainous areas between watercourses. The new study indicates that these regions were also home to large populations capable of modifying the forest and cultivating the land.
“These peoples did not only occupy the large rivers, rich in fish and easy to navigate by canoe,” explains Ranzi. “They knew the territory well, settled far from waterways and traveled on foot along these routes. »
“And it completely changes our understanding of how the Amazon has been occupied.” »
We used AI to help translate this article, originally written in English. A BBC journalist checked the translation before publication. Learn more about how we use AI.
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