Hundreds of Geoglyphs Discovered Beneath the Amazon Canopy

Deforestation has exposed hundreds of massive earthworks carved into the Amazon floor, and now LiDAR technology is finding even more hidden beneath the canopy. A landmark study published in the Proceedings of the National Academy of Sciences in 2022 used airborne laser scanning to reveal over 450 previously unknown geoglyphs in Acre state, western Brazil. The structures, some dating back more than 2,000 years, suggest that far more people once lived in the Amazon than previously believed.

How were the Amazon geoglyphs discovered?

The first major wave of geoglyph discoveries came by accident. In the 1970s, Brazilian geographer and archaeologist Alceu Ranzi spotted geometric patterns from aircraft flying over Acre state, a remote region in western Brazil near the Peruvian and Bolivian borders. He identified dozens of circular and square earthworks, but the dense rainforest made systematic study almost impossible at the time.

The second wave came in the 2000s, when large-scale cattle ranching and soy farming cleared vast swaths of Acre's forest. Between 2001 and 2018, roughly 8,000 square kilometers of tree cover vanished in the state, exposing more than 450 geoglyphs that had been invisible for centuries. Ranchers stumbled on them while plowing fields, and archaeologists scrambled to document what was being uncovered and, in many cases, destroyed.

The breakthrough that changed everything was LiDAR. A team led by archaeologist José Iriarte of the University of Exeter, working with Brazil's National Institute of Indigenous Lands (FUNAI) and the Brazilian Institute of Geography and Statistics (IBGE), flew a laser-equipped aircraft over 200 square kilometers of intact forest in 2019 and 2020. The pulses penetrated the canopy and produced detailed topographic maps of the ground below, revealing structures invisible to satellite imagery.

The LiDAR data uncovered 454 new geoglyphs in addition to the 48 previously known sites in the survey area. That density, roughly one earthwork every 0.44 square kilometers, suggests the region was far more intensively occupied than anyone realized. The researchers also found evidence of roads connecting geoglyph clusters, indicating coordinated settlement patterns rather than isolated structures.

The PNAS study on Amazon geoglyphs

What do the geoglyphs look like?

The structures range from small circular ditches roughly 50 meters across to enormous square enclosures spanning more than 300 meters on each side. Some are connected by straight earthen roads, forming networks that stretch for kilometers. Many feature deep ditches up to 4 meters wide and 2 meters deep, with raised embankments that may have supported wooden palisades.

The shapes fall into two main categories. Circular enclosures are the most common, often featuring a single ditch with an opening or causeway on one side. Square and rectangular structures tend to be larger and more elaborate, sometimes with internal divisions that suggest they served as communal gathering spaces or ceremonial plazas.

• Circular ditches: 50 to 200 meters in diameter, the most widespread form
• Square and rectangular enclosures: up to 350 meters across, often connected to roads
• Linear earthworks: straight causeways linking clusters of structures
• Combined forms: nested circles inside squares, or multi-ditch complexes

Who built the geoglyphs and when?

Radiocarbon dating places most of the Acre geoglyphs between 1,000 BCE and 300 CE, making them roughly contemporary with the Roman Empire. Some structures may be even older. The people who built them were likely part of complex, sedentary societies that practiced agriculture, managed forest resources, and organized large-scale communal labor. Earlier theories held that the Amazon was a pristine wilderness before European contact; these earthworks tell a different story.

The builders created their earthworks using only stone and wooden tools, moving thousands of cubic meters of earth by hand. The precision of the geometric shapes, particularly the near-perfect circles, suggests sophisticated surveying knowledge. Some researchers have compared the labor investment to that required for early European megalithic monuments, though the Amazonian structures are far less well known.

The builders are not known by name. Unlike the Maya or the Inca, they left no written records, and no living communities have claimed direct descent from the geoglyph builders. Archaeologists refer to the culture generically as pre-Columbian Amazonian societies. The Panoan-speaking peoples who have lived in the Acre region for centuries may be their distant descendants, but direct lineage remains unconfirmed.

Ancient Amazonian societies and their legacy

Why is this discovery so significant?

The implications reach far beyond archaeology. For decades, the dominant scientific narrative held that the Amazon was too nutrient-poor and too remote to support large, complex societies. The geoglyphs, along with similar discoveries across the basin, prove that pre-Columbian populations built monumental earthworks, managed vast tracts of forest, and sustained communities for centuries.

The LiDAR study estimated that the density of earthworks in Acre could rival that of better-known archaeological landscapes in Mesoamerica and the Andes. If similar structures remain hidden under the 5 million square kilometers of intact Amazon forest, the total number of ancient sites could be orders of magnitude higher than what has been documented so far. The Amazon, long imagined as a green void, may have been a populated, managed, and modified landscape for millennia.

What satellite imaging reveals about ancient civilizations

Deforestation and archaeological discovery in the Amazon

How does deforestation create both risk and discovery?

The geoglyphs exist in a paradox. Deforestation exposes them to archaeologists for the first time, but it also destroys them. Once the forest cover is removed, the thin tropical soils erode quickly, rain washes away exposed embankments, and ranchers plow directly through structures that survived for two millennia. Several sites documented in the 2000s had already been destroyed by the time archaeologists arrived to study them.

Acre state lost approximately 2,500 square kilometers of primary forest between 2019 and 2023, driven largely by illegal cattle ranching (Global Forest Watch, 2024). Brazil's deforestation rate surged during the Bolsonaro administration and has only partially recovered under the Lula government's renewed enforcement efforts. Every year of delay pushes more earthworks beyond the reach of preservation.

The paradox cuts deeper than logistics. Many of the geoglyphs sit on land that was cleared specifically because it was flat and well-drained, qualities that also made it attractive for ancient builders. The same geographic advantages that drew pre-Columbian engineers to a site now make it prime real estate for cattle ranchers and soy farmers, creating a direct collision between past and present land use.

What protection do the sites have?

Protection is minimal. Brazil's cultural heritage laws theoretically shield archaeological sites from destruction, but enforcement in remote Amazonian states is weak. Acre has no dedicated archaeological survey covering its entire territory, and FUNAI, the indigenous lands agency, has limited resources to monitor geoglyphs outside formally demarcated indigenous reserves.

Some sites have been fenced off or incorporated into small protected areas, but the majority remain on private ranchland with no legal restrictions on land use. Unlike Machu Picchu or Tikal, the Amazon geoglyphs have no tourism infrastructure, no UNESCO listing, and no international name recognition. They are among the most important archaeological discoveries of the 21st century, and most people have never heard of them.

The lack of protection is partly a visibility problem. Geoglyphs are earthworks, not stone temples. They do not photograph well from the ground, and they lack the dramatic profile that attracts tourists and media attention. A circular ditch in a cattle pasture does not compete with Angkor Wat for public imagination, even if it is equally significant for understanding human history.

What comes next for Amazon geoglyph research?

The LiDAR scans covered only a tiny fraction of the Amazon basin. The research team has called for expanded aerial surveys across Rondônia, Mato Grosso, and parts of Peru and Bolivia, where similar earthworks are suspected but unconfirmed. Advances in drone-mounted LiDAR and satellite-based synthetic aperture radar could eventually map the entire basin from the air.

There is also growing pressure to develop faster, cheaper methods for identifying and protecting sites before deforestation reaches them. Machine-learning algorithms trained on existing LiDAR data are being tested to automatically detect geoglyph-like patterns in satellite imagery, potentially flagging sites for protection before loggers and ranchers arrive.

International funding agencies and conservation organizations are beginning to recognize the value of protecting archaeological sites as part of forest conservation. The argument is simple: if ancient earthworks prove that the Amazon supported large, sophisticated societies, then the forest is not just an ecological resource but a cultural one, and its destruction erases human history along with biodiversity.

For now, the geoglyphs of Acre stand as a reminder that the Amazon's history is far richer and more complex than anyone imagined a generation ago. The dense canopy that hid these structures for centuries also preserved them. As the forest recedes, the question is not just what else we will find, but whether we will protect it in time.

How deforestation is reshaping the Amazon

The AI tools that are transforming archaeological research

Key takeaways

• LiDAR revealed 450+ geoglyphs hidden beneath the Amazon canopy in Acre state, western Brazil
• The structures date from roughly 1,000 BCE to 300 CE, built by complex pre-Columbian societies
• Deforestation simultaneously exposes and destroys the sites, with thousands of square kilometers lost since 2000
• Protection is minimal, with most geoglyphs on private ranchland and no UNESCO or national park status
• Expanded LiDAR surveys across the basin could reveal thousands more sites if conducted before further deforestation

• PNAS: LiDAR reveals pre-Columbian geoglyphs in the western Amazon
• University of Exeter: Amazon geoglyph discovery
• Global Forest Watch: Acre deforestation data
• PNAS: Deforestation and archaeological discovery
• FUNAI: Brazilian indigenous lands agency
• Why the Amazon was not a pristine wilderness