In a revelation upending views of the Amazon as pristine wilderness, scientists uncovered hundreds of ancient earthworks beneath the rainforest canopy—structures serving as pre-Columbian ceremonial sites. Using lidar technology mounted on an aircraft, researchers scanned roughly 4,500 square kilometres of forest in Brazil’s Acre state, near the borders with Bolivia and Peru.
The laser pulses pierced the dense vegetation and revealed 396 new earthworks, many of them geometric geoglyphs—precise ditches, embankments and enclosures stretching across areas the size of several football fields. The findings, published in Nature, suggest the broader Southwest Amazon may conceal between 24,000 and 30,000 such structures in total.
These monumental features are the signature of the Aquiry people, who flourished in the region from about 600 BCE to CE 850. Many of the newly mapped sites date to roughly CE 100–300, a period when the civilisation appears to have reached its height.
Archaeologists believe the geoglyphs were not primarily defensive or residential but held ceremonial or cultural significance—venues for festivals, rituals or communal gatherings whose exact purpose remains debated.
Lead author Martti Pärssinen, an emeritus professor at the University of Helsinki, said: “We were surprised that we found about 10 times more of the geoglyphs than we ever thought.”
Based on the density and distribution of the sites, the team estimates the Aquiry population may have peaked at around three million people and occupied an area of some 183,000 square kilometres—comparable in size to the US state of North Dakota.
The discovery carries sweeping implications. It challenges the notion of the Amazon as an untouched “virgin” forest and suggests that pre-colonial populations across the basin could have numbered in the tens of millions. Mr Pärssinen noted: “What we have studied represents less than 3 % of the whole Amazonia,” adding that similar high-density zones are likely waiting to be found elsewhere.
Independent experts have hailed the work while urging caution. Heiko Prümers of the German Archaeological Institute called the study “really fascinating” for correcting the myth of an empty rainforest.
However he questioned whether some clustered features were counted separately or combined, and whether frequent settlement shifts rather than permanent high population density might explain the abundance of sites.
Beyond rewriting demographic history, the findings offer a provocative lesson for the present. Modern human activity has already degraded roughly one-third of the Amazon and fully cleared about 17 %. Two millennia ago, the Aquiry appear to have engineered the landscape on a vast scale while maintaining ecological balance. Mr Pärssinen said: “We could learn something about how they managed the forest in the past.”
The lidar survey covers only a fraction of the Amazon’s vast expanse. As more flights and ground excavations follow, the scale of ancient human presence—and the ceremonial landscapes they left behind—may prove even more astonishing than today’s stunning discovery.