A study in Nature estimates that at the height of the Akiri culture, in the first to third centuries AD, 1.25–3 million people lived in southwestern Amazonia. The findings challenge the image of a forest that was almost empty of people before the European conquest.
Under the forest canopy of the Southwest Amazonia Hidden beneath the surface is a landscape shaped over centuries by large, organized populations. Research based on aerial laser scanning suggests that a network of more than 183 public, ceremonial, and political centers existed across an area of about 20 square kilometers, and that between 1.25 and 3 million people lived in the area at its peak.
The study, published on July 29, 2026 in the journal Nature, was led by Professor Emeritus Martti Parsinen fromUniversity of Helsinki, in collaboration with researchers from Finland, Brazil, Peru, Leopard and other institutions. The researchers call the multicultural complex that built the earthworks Aquiry, after an indigenous name for the Acre River.
It was not a single kingdom with a central government, but rather a network of different communities that shared cultural traditions and worldviews. The name Akiri is also a research term: it is not known what these communities called themselves or what languages they spoke.
The forest hid the buildings—the laser revealed them
The geometric earthworks of western Amazonia have been known to archaeologists for decades. However, many of them were discovered in the areas where they were created, because dense vegetation makes it difficult to identify canals, embankments, and roads in aerial and satellite photographs.
To overcome the obstacle, the team usedLidar — A system that transmits laser pulses from an aircraft and measures their return time. Some of the pulses penetrate between the leaves and hit the ground, making it possible to build a 3D model of the surface beneath the vegetation.
In 2024, researchers flew about 4,430 kilometers and scanned about 4,500 square kilometers in the states of Accra andAmazon In Brazil, 432 were recorded in the ten scanning lanes. Earthworks, and only 36 of them were previously known. In open areas where the methods could be compared, LiDAR identified five times more buildings than satellite imagery.
Among the finds were square, circular, and polygonal enclosures, canals, embankments, and straight roads. The size of most of theGeoglyphs Ranges from 0.35 to 14 hectares, while the largest known site covers almost 50 hectares.
More than 20 centers — but this is an estimate
The researchers combined the lidar data with satellite imagery, previous surveys, and carbon-14 dating. According to various models they presented, in the field Akiri culture There may be between 23,760 and 29,500 earthen structures. The article's cautious title suffices to state that their number exceeds 20.
It is important to emphasize that not all structures were directly detected. Most of the number is an extrapolation from the scanned strips to large unscanned areas, distinguishing between high-density areas and sparser marginal areas.
The population estimate is also not a census of residents. Carbon dating suggests that about 25% to 60% of the centers were active at the same time during the peak period, roughly between 100 and 300 AD. Assuming that the construction and maintenance of an average center required about 300 people, an estimate of 1.25–3 million residents was obtained. The researchers note that the difficulty of identifying structures under the canopy may increase the number, but they chose to present the more conservative range.
The findings do not depict densely populated cities in the style of ancient Rome. Many of the complexes were probably not used for permanent residence or defense, but rather were centers where dispersed communities came for ceremonies, meetings, political decisions, feasts, dancing, music, and games.
A culture without stone ruins
The absence of stone structures contributed to the fact that the extent of the culture was not understood for a long time. The area has no sources of stone suitable for monumental construction, and the most prominent remains are ditches and earthen embankments. Some of the ditches are 9–13 meters wide and up to five meters deep—constructions that required planning, division of labor, and geometric knowledge.
Chronological models indicate the construction of geoglyphs from about 600 BC to 850 AD, with regional differences. Later, after 1000, villages surrounded by circular mounds also appeared in the area. The researchers distinguished between the later villages and the monumental centers of Akiri.
It is not known why the construction of the centers ended around the ninth century, or whether it was a sudden collapse, a gradual social change, or a transition to a different settlement pattern. The chronological parallel to the decline of Maya centers is interesting, but does not provide an explanation, and the current study does not establish a connection between the processes.
A forest shaped by man
The findings add to research showing that the Amazon before the European conquest was not a natural space unaffected by humans. The Akiri people cleared areas of bamboo forest to grow corn, squash and cassava, establish centers and pave roads. They also engaged in horticulture and the cultivation of useful trees, including the Brazil nut and peach palm.
This activity may have an impact that is still evident today in the composition of tree species, soil and biodiversity. The researchers suggest that ancient human activity should also be taken into account when reconstructing the carbon balance of the Amazon. However, they frame this as a possible outcome: Only if similar patterns are found in other regions will it be necessary to revise population estimates and climate models more broadly.
The study does not present the forest as a purely human creation, but demonstrates a long biocultural history: natural ecosystems and human communities have influenced each other for thousands of years. Recognizing this history changes not only the story of pre-Columbian cultures, but also the starting point for research and conservation of the Amazon today.
Questions and Answers
What did the lidar scans reveal?
The scans documented 432 earthworks along the ten flight paths, only 36 of which were previously known. Combining the data with surveys and satellite imagery led to an estimate of more than 20 centers in each Akiri culture area.
Did three million people really live in the area?
This is an upper bound estimate, not a direct count. The researchers estimated how many centers were operating simultaneously and how many people were required to build and maintain each one, arriving at a range of 1.25–3 million inhabitants in 100–300 AD.
Were these big cities?
Not necessarily. The study describes a model of a population dispersed around public and ceremonial centers, rather than dense urban concentrations. The centers were likely used for gatherings, ceremonies, and decision-making.
Why did Akiri culture disappear?
The reason is unknown. The construction of the centers declined around 850 AD, but there is not yet enough evidence to determine whether a crisis, social change, or a transition to a different form of settlement occurred.
More on the subject on the science website
- 12,500 Years: Ancient Art in the Amazon Reveals Secrets of Prehistoric Ecology
- When the drought didn't appear: Lake sediments challenge the accepted explanation for the collapse of Maya civilization
- Who lives in Machu Picchu? DNA analysis shows surprising diversity in the ancient Inca palace
- The Nazca people who painted the giant drawings on the plains, visible only from the air, became extinct because of a plant
- Exposing the Myth of “Environmental Self-Destruction”: The True Story of Easter Island
For the scientific article: Opening the scientific article
