Hidden beneath the dense canopy of the Amazon rainforest, ancient geometric earthworks have been brought to light by lidar technology, revealing the scale of a pre-Columbian civilization in Southwest Amazonia. The structures, known as geoglyphs, were built by the Aquiry civilization and include ditched enclosures that served as ceremonial and political centers.
In 2024, lidar surveys covered 4,497 km² across the states of Acre and Amazonas in Brazil. The surveys documented 432 earthworks, of which only 36 were previously known, according to the research.
Documented by lidar; only 36 were known before.
The Aquiry civilization, named after the region, built geoglyphs over a vast area of approximately 183,000 km². The geoglyphs range in size from 0.35 to 14 hectares, with the largest nearly 50 hectares. Their ditches are 9–13 meters wide and up to 5 meters deep.
Researchers estimate that the total number of earthworks across the entire region may exceed 20,000, with a specific range of 24,000–30,000. About two-thirds of these are attributed to the Aquiry civilization. The known earthworks in the study area grew from 60 to 200 to 1,279 over successive surveys.
The Aquiry civilization peaked between 100–300 AD, with about 60% of structures in use simultaneously. During that period, the population of the Aquiry region is estimated at 1.25 to 3 million people. This figure is part of a broader reassessment: pre-Columbian population estimates for Greater Amazonia (about 6.7 million km²) have been revised upward to 5–10 million, from earlier estimates of 1.5–2 million.
The studied area represents less than 3% of the entire Amazon rainforest. The interfluvial hinterland (terra firme), which covers more than 90% of Amazonia, appears to have supported relatively dense human populations, challenging traditional views of the region as sparsely inhabited.
Most earthworks detected—92%—were within 210 kilometers of Rio Branco, while 8% were near Lábrea. Lidar penetration was about 10% lower in the Lábrea area due to denser forest, and a significant portion of the surveyed ground lacked sufficient point clouds for visualization.
The Aquiry civilization practiced intensive agroforestry, promoting beneficial tree species such as Brazil nut and edible palms. They intentionally burned bamboo-rich land to maintain soil fertility, a practice that may explain ancient charcoal layers previously attributed to natural fires. Researchers suggest these findings call for a reassessment of South America's pre-Columbian population density and its impact on soil and biodiversity.
Construction of an average geoglyph would have required about one year of work by a group of 300 people, assuming each adult moved one cubic meter of soil per day.