Millions once lived here. Laser technologies reveal the scale of a lost Amazonian civilization

"These people were creating monumental geometry in the Amazon at the same time Pythagoras was formulating his theorem in Greece," says paleontologist Alceu Ranzi, president of the Institute of Amazonian Geoglyphs and a member of the research team.

Scanning the Past

The study, recently published in the journal Nature, was conducted by a group of scientists from universities and institutes in Spain, Finland, Brazil, and Denmark.

They scanned the dense forest canopy using LiDAR (Light Detection and Ranging) technology, which uses laser pulses to measure distances and create complex three-dimensional maps. This allows for the analysis of large areas without clearing vegetation or physically visiting every site.

Павялічыць

"This was the first truly large-scale study using LiDAR technology in the Amazon," says archaeologist, anthropologist, and co-author of the work Martti Pärssinen from the University of Helsinki.

The team studied an area of 4400 sq. km and found 432 geoglyphs — the vast majority of which had not been previously recorded. They were created between 600 BC and 850 AD.

The Acre civilization, to which these geoglyphs belong, is estimated by scientists to have occupied an area of about 183,000 square kilometers — roughly the size of modern Cambodia or Syria. During its flourishing period (100–300 AD), the population could have reached three million people.

According to Alceu Ranzi, researchers found ditches up to 15 m wide and 5 m deep. Such grandiose structures indicate that they were created by large communities acting collectively.

"There is no stone in this region. They probably used wooden tools and baskets to move the soil," he suggests.

However, due to the humid climate of the Amazon, organic materials decompose quickly, making definitive conclusions quite difficult.

Researchers suggest that the construction of such objects required not only enormous labor costs and division of labor but also deep knowledge in mathematics and geometry.

What were they created for?

It was once believed that geoglyphs served as fortresses or defensive structures protecting the population from invasions.

Павялічыць

However, today experts believe that these structures most likely performed ceremonial and political functions — serving as gathering places rather than permanent residences.

"If this is confirmed… it means these people lived in peace. The fact that they spent so much effort and labor creating [geoglyphs] suggests that they had no serious enemies to worry about," says Ranzi.

According to Pärssinen, the Acre culture was characterized by deep respect for nature.

"They never turned the rainforest into savanna," he says. "Forest clearing and tree felling were done only on the scale necessary to sustain their way of life — growing corn, pumpkins, and cassava — and no more."

The results of the excavations indicate that the structures were meticulously maintained.

"It wasn't just about construction, but about preserving these objects for centuries, which undoubtedly required extensive accumulated knowledge," notes another co-author of the study, archaeologist and anthropologist Rhuan Carlos Lopes from the Federal University of Pará (Brazil).

Павялічыць

According to Ranzi, the geoglyphs were not isolated and hidden in the forest; they were interconnected.

"We mapped 350 kilometers of roads connecting the geoglyphs," he explains. "These paths led to them, and as one approached the structures, the roads became wider."

The End of the Acre Civilization

The creation of geoglyphs apparently ceased around 850 AD. The reason for this remains unclear.

Ranzi draws a parallel with the Maya civilization: the major centers of this culture in Mexico and Central America were abandoned around the same time.

"The Maya stopped building and using palaces. The pyramids of Yucatan were swallowed by the forest," he notes. "Something similar happened in the Amazon. Perhaps the 9th century was a period of a large-scale natural crisis."

New research, including this study, challenges the ingrained notion that the Amazon rainforests were "wild nature" that had never known human presence.

Павялічыць

Over the past decades, interdisciplinary studies have shown that long before the arrival of Europeans, millions of people lived here, leaving a significant mark and transforming the landscape of the world's largest tropical forest.

"What we see in the Amazon is not a vast natural forest, but rather a huge historical garden, shaped by human activity," asserts Lopes.

Estimates of the region's population in the pre-colonial era are constantly being revised upwards. While early studies suggested that 1–2.5 million people lived in the entire Amazon, later estimates raise this figure to 5–10 million.

Now, given that up to three million people could have lived in a relatively small area, these figures may need to be revised once again.

Furthermore, it was previously thought that the inhabitants of the region settled mainly along large rivers, where it was easier to obtain food.

However, geoglyphs are found primarily on elevated areas located between rivers. The new research indicates that a large number of people also lived in these areas, cultivating agricultural crops and altering the forest landscape.

"These people were not confined to the banks of large rivers, rich in fish and convenient for canoe travel," says Ranzi. "They had an excellent understanding of the landscape, settled away from rivers, and moved overland using a network of roads. And this completely changes our understanding of how the Amazon was settled."

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