Laser scans keep exposing lost cities hidden beneath the Amazon canopy

For centuries, explorers who went looking for lost cities in the Amazon rainforest either turned back empty-handed or vanished trying. Thick canopy, remote terrain and a landscape that swallows ruins within a few decades of abandonment made ground-based archaeology painfully slow across a river basin roughly the size of the contiguous United States. A laser-based mapping technique has now done in a matter of flights what generations of ground survey could not, repeatedly revealing that the rainforest floor is covered with the remains of complex societies nobody suspected were there.

The pace of new discoveries has forced archaeologists to continually revise assumptions that stood largely unchallenged for decades, since each additional survey adds sites faster than researchers can fully study the ones already found. That backlog has itself become part of the story, as newly identified earthworks now outnumber the teams and funding available to excavate and interpret them in the near term.

How Airborne Lidar Cuts Through the Canopy

The tool behind these discoveries is lidar, short for light detection and ranging, a remote-sensing method that fires hundreds of thousands of laser pulses per second from an aircraft toward the ground and measures how long each pulse takes to bounce back. Enough of those pulses slip through gaps in the leaves to strike the actual earth beneath a forest, and software can then filter out every point that bounced off vegetation, leaving a bare-earth model of the terrain. The technique, which is also used in surveying, geology and forestry, gives archaeologists what amounts to a digitally deforested map, a capability described in detail in the technical background on how the sensors work. It replaced years of machete-and-compass fieldwork with flights that can cover dozens of square miles in a single pass.

Bolivia’s Casarabe Cities: Cotoca and Landívar

One of the clearest demonstrations came from Bolivia’s Llanos de Mojos region, where a team led by Heiko Prümers of the German Archaeological Institute flew lidar over six survey areas covering the heartland of the Casarabe culture, a society that flourished there between roughly 500 and 1400 AD. The scans identified 26 distinct sites, including 11 that had never been recorded, and revealed that two of them, called Cotoca and Landívar, were full urban centers spanning half a square mile and 1.2 square miles respectively. Each city was ringed by successive moats and ramparts and built around earthen platforms and conical pyramids more than 70 feet tall, all oriented in the same compass direction. Raised causeways radiated outward from the centers for miles, linking smaller satellite settlements the way spokes connect to a wheel, while canals tied the whole system to nearby rivers and a lake that supplied water to Cotoca, according to the findings reported after the survey’s publication. The Casarabe also built massive water reservoirs whose purpose remains debated, and their occupation of the region appears to have ended around 1400, before European contact, in a collapse researchers suspect was tied to prolonged drought.

Brazil’s Aquiry Civilization Triples the Known Footprint

A separate survey flown over the Brazilian states of Acre and Amazonas produced an even larger jump in scale. Researchers logged more than 4,400 kilometers of airborne lidar transects and identified 432 earthworks in the surveyed strips, of which only 36 had been previously documented on the ground. Extrapolating from that density, the team now estimates between 24,000 and 30,000 monumental earthworks exist across the wider region, built by a society researchers have named the Aquiry civilization between about 600 BC and 850 AD. The geometric ditched enclosures, embankments and ceremonial complexes the surveys found suggest the Aquiry territory covered roughly 183,000 square kilometers, about three times the area earlier estimates assumed, and researchers calculate the land could have supported between 1.25 million and 3 million people at its peak between 100 and 300 AD, a scale detailed in coverage of the study’s publication in the journal Nature. Evidence at the sites points to residents cultivating maize, squash, manioc, beans and peanuts alongside managed stands of Brazil nut and peach palm trees.

Why Population Estimates for the Basin Keep Rising

Both surveys point to the same underlying correction: earlier population estimates for the pre-Columbian Amazon were built almost entirely on what ground teams could physically find, and ground teams could only find sites the forest allowed them to see. Lidar’s ability to detect roughly five times more earthworks than satellite imagery alone can spot means each new survey tends to multiply, rather than modestly adjust, the previous count. The ceremonial and geometric nature of many structures found in Brazil, built in circular, square and multi-sided layouts rather than as defensive works, also argues against the old assumption that dense population required either agriculture-poor soil or constant warfare to explain its absence from written history. Both the Bolivian and Brazilian cases instead show societies that reshaped their landscapes deliberately, through canals, causeways, planted orchards and engineered water systems, well before any European set foot in the basin. Each new flight path effectively tests the same hypothesis in a new location, and so far the pattern has held: wherever researchers point a lidar sensor at unsurveyed Amazon forest, another piece of a much larger population turns up beneath the canopy.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.