Laser technology finds 432 geoglyphs of an ancient civilisation deep in the Amazon, home to millions

Researchers have discovered hundreds of earthworks hidden deep in Brazil’s Amazon jungle. They believe the structures were built by an ancient civilisation of millions of people.

These vast structures, dug into the earth beneath the dense forest, are known as geoglyphs. They were built thousands of years ago in an area far from the main rivers.

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

The researchers scanned the canopy of the dense forest using LiDAR (Light Detection and Ranging) technology. The technology uses laser pulses to measure distances and creates complex three-dimensional maps. This made it possible to analyse a vast area without cutting vegetation or physically visiting every site.

“This was the first truly ambitious LiDAR survey in the Amazon,” said Martti Pärssinen, an archaeologist and anthropologist at the University of Helsinki and a co-author of the paper.

The team surveyed an area of 4,400 square kilometres. They identified 432 geoglyphs, most of which had never been documented before. They were built between 600 BC and AD 850.

The researchers estimate that the so-called Acre civilisation, which built them, spread across about 183,000 square kilometres — roughly the size of Cambodia or Syria.

At its peak between AD 100 and 300, the civilisation may have had around three million inhabitants, the researchers believe.

Alceu Ranzi, a palaeontologist who heads the Amazon Geoglyphs Institute and is a member of the research team, said, “While Pythagoras was developing his theorem in Greece, these people were creating enormous geometric artworks in the Amazon.”

Ranzi said the team found ditches up to 15 metres wide and five metres deep. Such massive structures point to the collective effort of large communities.

He believes that, as there is no stone in the region, wooden tools and baskets were probably used to carry earth. However, because organic material decays quickly in the Amazon’s humid climate, it is difficult to know for certain.

According to the researchers, alongside a huge workforce and a division of labour, the construction work required considerable knowledge of mathematics and geometry.

It was previously thought that Amazonian populations lived mainly along the banks of the big rivers, where food resources were easier to obtain. But the geoglyphs are located mainly on the higher ground between the rivers. The new study suggests these regions were also home to large numbers of people who were able to alter the forest and cultivate crops.

“These people did not live only along the main rivers for the abundance of fish and the ease of travelling by canoe,” Ranzi said. “They understood the landscape, settled away from the rivers and moved along these paths on foot.” That completely changes the understanding of how the Amazon was occupied, he says.

This study, along with other recent research, challenges the long-held belief that the Amazon rainforest was an uninhabited wilderness. Research in recent decades has shown that millions of people lived here long before the arrival of Europeans and left a lasting mark on the shape and structure of the world’s largest tropical forest.

“What we see in the Amazon is not a vast natural wilderness, but a vast historical park shaped by human activity,” argues Lopes, a researcher involved in the study.

Estimates of the region’s pre-colonial population have kept rising. Earlier research suggested the whole Amazon could support one to two and a half million people; later estimates raised that figure to between five and ten million. Now that a comparatively small area may have held up to three million inhabitants, those figures may need to be revised upward again.

According to the researchers, the ninth century may also have been a time of greater environmental crisis in the Amazon. Just as the pyramids of Yucatán were swallowed by the forest, the same kind of event happened in the Amazon, they noted.