With flights over Acre, scientists find almost 400 new geoglyphs in the Amazon. New research co-authored by Brazilian scientists has revealed structures left in what is now the junction of the states of Acre and Amazonas by a civilization of millions of people that inhabited the southwest of the Amazon between 600 BC and 850 AD. The discovery, published in the magazine "Nature", challenges what was known about the population density and cultural complexity of the Amazon region. The Aquiry civilization, a name derived from the indigenous term for the Acre River, built large centers for political and ritual purposes that cover around 183 thousand square kilometers, a territory almost the size of Paraná. Its remains are enigmatic geometric figures on the ground: spaces delimited by ditches several meters deep, connected to each other by straight paths. READ ALSO: With flights over Acre, scientists find almost 400 new geoglyphs in the Amazon Various types of earthworks with their topographic contexts. Reproduction/Martti Pärssinen More than 400 sites identified, but there could be thousands Archaeologists found traces of more than 400 well-preserved sites. But they estimate that there may have been more than 20,000 ancient ceremonial centers in the region. That's far more than previous estimates of 10,000 for the entire Amazon, noted Science magazine. The largest of the sites discovered by the researchers occupies 50 hectares, the equivalent of 70 football fields. "What surprised us most was the extraordinarily high number of geoglyphs [large figures made in the ground] and other earthen constructions found in an area that represents less than 3% of the Greater Amazon," lead author, archaeoanthropologist Martti Pärssinen, from the University of Helsinki, told Science Alert. READ ALSO: Strange beehive shapes cover a vast area of ??Mars; see IMAGE Geoglyphs in the Amazon Archive/Altino Machado The Amazon may have had tens of millions of inhabitants The new study estimates that between 1.25 million and 3 million people lived there at the beginning of the first millennium. The data challenges previous estimates about the population of the entire Amazon region, which ranged between 1 and 10 million. According to the authors, the total population of the Amazon may have reached tens of millions of people: "Our discoveries cause a reversal in what we knew about the past of the Amazon region", says Pärssinen, in a statement from the University of Helsinki. And he adds: "Many other regions of the Amazon may have been much more densely populated and have undergone a much more intense transformation than previously assumed." Civilization of farmers and builders The Aquiry also left their mark on the plant landscape. They burned bamboo forests to open up areas for growing corn, pumpkin, and cassava, as well as building their ceremonial centers and the wide paths that led to them. They also managed tree species of high cultural value, promoting their propagation to the detriment of other species. "The human impact on the Amazon environment was much greater than previously believed", highlights Pärssinen. "Civilization also altered the production and carbon balance of the ancient Amazon, something that should be better considered in future climate models." The laser scanner that passes through the forest The hidden structures beneath the Amazon rainforest were revealed thanks to Lidar, an aerial laser mapping technology that passes through gaps in the vegetation and bounces off the ground, allowing three-dimensional maps of the landscape to be reconstructed. "We flew in long, straight sections of around 450 km, mapping a strip approximately one kilometer wide every ten kilometers. This allowed us to cover as large a continuous area as possible," explains co-author Juha Hyyppä from the Finnish Geospatial Research Institute. What did the indigenous people do in the mapped places? The structures with geometric shapes and straight paths were probably centers built to strengthen relationships between communities, serve as meeting points for political decision-making or for demonstrations of generosity by chiefs. Ceremonies included ritual dances, music, banquets, athletic competitions, and ball games. “Its variable dimensions, shapes, construction methods and locations reflect the distinct geographic and cultural characteristics of the region,” highlights Risto Kalliola, professor at the University of Turku, Finland. Speaking to the Science portal, Brazilian and indigenous anthropologist Francisco Apurinã, who participated in the study, said that his people in Acre recognize geoglyphs as a type of "kymyrury": spaces that function as "houses for spirits". A civilization without stone ruins Relatively little is still known about the Aquiry. It is unknown, for example, which languages ??were spoken in these communities or how their inhabitants called themselves. The region lacked stone, so no lithic ruins remained. However, Amazonian geoglyphs help us understand how they lived. "It was not a single kingdom, but a network made up of many different communities", says another author of the study, Pirjo Kristiina Virtanen, professor of Indigenous Studies at the University of Helsinki. Disappearance is an enigma The biggest mystery remains the disappearance of the Aquiry: "There are still many unanswered questions. One of the most important is what happened between approximately 850 and 1000 AD. Why did this civilization disappear?", asks Pärssinen. The question gains even more force when considering the global context: around the same time, the Classic Maya civilization in Central America also gradually collapsed, although the causes of both collapses remain the subject of debate.