Archaeologists have uncovered nearly 400 ancient earthworks beneath the dense canopy of the southwestern Amazon, revealing complex societies that existed in the rainforest more than a millennium before European colonization. The discovery, detailed in a recent study published in the journal Nature, challenges longstanding assumptions that the Amazon was a largely untouched wilderness prior to the arrival of Spanish and Portuguese explorers in the 15th century.

Using lidar technology, which emits laser pulses to penetrate the thick forest cover, researchers were able to map an extensive series of geoglyphs—large geometric shapes formed by embankments, mounds, and trenches. These earthworks, which range in size from about seven acres to over 120 acres, are concentrated near the borders of Bolivia, Brazil, and Peru. They date from roughly 600 B.C. to 850 A.D. and are connected by a network of ancient roads.

The findings point to a sophisticated pre-Columbian society, referred to by the research team as the Aquiry culture, which inhabited a region spanning approximately 1,700 square miles. Based in part on oral histories from the Apurinã people who live near the sites, the study suggests the geoglyphs served multiple functions, including ceremonial activities, political gatherings, music and dance events, and ball games. However, no evidence has been found to indicate permanent settlements at these mound sites, nor that they had a defensive purpose.

Experts not involved in the study described the work as a significant contribution to understanding Amazonian history. “This is an important and ambitious study,” said José Iriarte, an archaeologist at the University of Exeter, noting the extensive lidar coverage revealed large-scale pre-Columbian landscape modifications previously unseen.

The discovery builds on historical accounts from early European explorers such as Gaspar de Carvajal, a 16th-century missionary who described densely populated areas and large settlements along the Amazon River. These narratives were largely dismissed for centuries due to the devastating impacts of disease and colonization on Indigenous populations, as well as skepticism about the ability of complex societies to thrive in the rainforest without European-style agriculture.

Recent archaeological work across the Amazon basin, including sites in eastern Ecuador, has uncovered networks of roads, canals, plazas, and residential platforms, indicating greater human impact on the forest than previously recognized. Researchers estimate there may be thousands more earthworks yet to be found, though the dense rainforest and ongoing deforestation complicate preservation efforts. “This heritage is highly threatened by logging and soybean farming,” warned Eduardo Neves, an archaeologist at the University of São Paulo.

At its peak around 100 to 300 A.D., the Aquiry society may have supported a population as high as three million people in this region alone, according to the research team. While some experts urge caution regarding these population estimates—due to the reliance on indirect calculations rather than excavated settlements—there is growing acceptance that early European observations of populous Amazonian societies were not exaggerated.

The study underscores a growing consensus that the pre-Columbian Amazon was home to dynamic, large-scale cultures who shaped the landscape in ways only now becoming fully visible through advances in remote sensing and archaeological methods.