A Civilization of 3 Million People Was Hidden in the Amazon

In 2002, Martti Parssinen flew over the state of Acre in Brazil. Through the aircraft window, he could see geometric earthworks etched into the ground below him: enormous ditched enclosures arranged in precise patterns, connected by straight roads, spread across a landscape that the world had classified as pristine rainforest. The scale of what he was looking at had not been visible before, and it kept growing the longer he flew. “It completely transformed my understanding,” Parssinen, an archaeo-anthropologist at the University of Helsinki, told ScienceAlert. “And made me realize how mistaken earlier assumptions had been.”

More recently, he felt something similar again. A new LiDAR survey, published in Nature on July 29, 2026, suggests that the civilization those earthworks belonged to was nearly ten times larger than what Parssinen had imagined even after that first flight. Between 600 BCE and 850 CE, something between 1.25 and 3 million people may have lived in the southwestern Amazon. They called their river the Aquiry. Researchers named the civilization after it.

What the Aquiry Built

The Aquiry civilization was not a single kingdom or empire. It was a diverse network of communities spread across the forests and savannas of southwestern Amazonia, in what is now the state of Acre in Brazil and the adjacent territories of Bolivia and Peru, connected by shared traditions, road systems, and the distinctive earthworks they left on the landscape. They produced no written records. Their dwellings were wooden and have long since decomposed. What survives is the shape of what they moved and arranged on the ground: ditches dug meters deep into the earth forming geometric enclosures, straight roads connecting sites across kilometers of terrain, and the altered composition of the forests they managed for centuries.

These geometric earthworks, known as geoglyphs, had been noticed in Acre when land was cleared for agriculture. Flights and ground surveys over previous decades had documented hundreds of them. What nobody had been able to determine was how many there were in total, because the dense forest cover made systematic survey impossible. Then LiDAR changed the equation.

Laser Pulses Through the Canopy

LiDAR, light detection and ranging, fires millions of laser pulses from an aircraft. Some of those pulses penetrate gaps in the forest canopy and reach the ground, bouncing back and allowing researchers to reconstruct the hidden terrain below with high precision. The technique has transformed Amazonian archaeology over the past decade, revealing earthworks and settlement systems that had remained invisible to satellite imagery and ground survey.

For the new study, Parssinen and his colleagues flew a series of transects totaling approximately 450 kilometers over a survey area of 4,497 square kilometers in southwestern Amazonia, representing less than 3 percent of Greater Amazonia’s total extent. Their complete dataset yielded 432 earthworks. Of those, 396 were previously unknown.

The density of the finds surprised the team. “What surprised us most was the extraordinarily large number of geoglyphs and other earthworks found within an area representing less than 3 percent of Greater Amazonia,” Parssinen said. “The scale of the archaeological record suggests that many other regions across Amazonia may have been far more densely populated and intensively modified than previously assumed.”

Extrapolating from the survey area to the known distribution of the Aquiry earthwork tradition, the researchers estimated that the southwestern Amazon may contain somewhere between 24,000 and 30,000 earthworks in total. Previous estimates for the entirety of Amazonia had placed the number around 10,000.

A Civilization the Size of North Dakota

From the density and distribution of the earthworks, the research team estimated that the Aquiry civilization may have covered approximately 183,000 square kilometers at its territorial peak, an area roughly comparable to the state of North Dakota. Within that territory, the population could have reached between 1.25 and 3 million people at the civilization’s apparent high point, around CE 100 to 300.

To place those numbers in context: previous estimates placed the entire pre-Columbian population of the Amazon basin at approximately 2 million people in total. The Aquiry study suggests that southwestern Amazonia alone may have held that many or more within an area that makes up only a small fraction of the basin.

What did that landscape actually look like? Parssinen described it to ScienceAlert. At the center of many clearings would have stood the large geometric earthworks, connected by broad and narrow roads. At certain times of year, these places would come alive with ceremonies, gatherings, music, dancing, athletic competitions, and other communal events. The earthworks themselves were surrounded by large wooden longhouses, fields of maize, manioc, squash, and cotton, and forests nearby rich with managed fruit and nut trees reflecting centuries of deliberate stewardship of the landscape.

What Remained in the Forest

The Aquiry left no writing. Their wooden architecture is gone. But two forms of evidence persist. The earthworks themselves have proven remarkably durable: ditches cut meters into the ground are difficult to erase even over centuries of forest regrowth. And the composition of the Amazon itself may carry the Aquiry’s agricultural legacy.

Researchers studying the Amazon’s vegetation have documented concentrations of domesticated and semi-domesticated plant species, fruit trees, nut palms, and useful shrubs in patterns that appear to trace ancient settlement and land use. The forest the world considers pristine wilderness was substantially shaped by the communities who managed it over the 1,500 years of Aquiry civilization. The distribution of useful trees in the southwestern Amazon is, in part, a map of where people once lived and what they chose to cultivate.

The Question of Disappearance

The Aquiry civilization appears to have declined and ultimately disappeared between approximately CE 850 and CE 1000. What happened is unknown. No written record explains it. The earthworks simply stop being maintained after a certain point, and the characteristic ceramic traditions associated with Aquiry sites are not found in later layers. Whether the cause was drought, epidemic disease, internal conflict, migration, or some combination of pressures that are no longer visible in the archaeological record, the answer remains open.

“One of the most important is what happened between approximately 850 and 1000,” Parssinen said. “Why did this civilization disappear?”

Between its disappearance and the arrival of European colonizers in the 16th century, the forest grew back over what the Aquiry had built. By the time Europeans described Amazonia, the earthworks were buried under vegetation, the wooden longhouses had long since decayed, and the population was a fraction of its former size. The Amazon that colonial sources described as an empty wilderness was an Amazon in recovery from a civilizational collapse that those same sources knew nothing about.

The End of the Pristine Wilderness

Parssinen is clear about the broader implication. The traditional view of the Amazon as pristine, essentially untouched wilderness, he argues, should be abandoned. The research now coming from LiDAR surveys across the basin is revealing a rainforest that was shaped by large human populations in ways that are still ecologically visible today.

That history also carries stakes for the present. Scientists estimate that if the Amazon loses more than approximately 20 percent of its vegetation cover, the region may no longer be able to sustain itself through its own moisture recycling. It has already lost more than 13 percent. Understanding that the current forest is partly the product of long-term human stewardship, and not simply a natural given, changes how researchers think about what needs to be protected and why.

The civilization Parssinen first saw from the air in 2002 is substantially larger than he thought then. It is almost certainly larger than the current study has established, since the survey area covers less than 3 percent of Amazonia and the Aquiry pattern is unlikely to be unique to one small region of the basin. What exists beneath the forest canopy of South America is still being discovered, one laser pulse at a time.

Sources

Parssinen, M. et al. (2026). [Aquiry civilization LiDAR survey study]. Nature. https://doi.org/10.1038/s41586-026-10835-7