An ancient, massive urban complex has been found in the Ecuadorian Amazon

Scientists have uncovered the Amazon’s earliest and largest example of farm-based citylike settlements high in the foothills of the Ecuadorian Andes.

The thousands of mounds, plazas, terraces, roads and agricultural fields — revealed for the first time in their fullest extent by airborne laser scans — necessitate a rethinking of just how complex ancient civilizations of the Amazon may have been, researchers report in the Jan. 12 Science.

Over the last decade or so, the use of light detection and ranging, or lidar, in archaeology has led to significant discoveries in tropical climates, where ancient settlements often lay obscured beneath dense jungle (SN: 12/4/23). In 2018, researchers released scans of remnants of Mayan settlements in Guatemala, followed by Olmec ruins in Mexico in 2021 and Casarabe sites in the Bolivian Amazon in 2022, all which have been revealed to be metropolitan-like settlements filled with complex infrastructure (SN: 9/27/18; SN: 1/6/23; SN: 5/25/22).

“It’s a gold rush scenario, especially for the Americas and the Amazon,” says Christopher Fisher, an archaeologist at Colorado State University in Fort Collins who has scanned sites throughout the Americas but was not involved in the new research. “Scientists are demonstrating conclusively that there were a lot more people in these areas, and that they significantly modified the landscape,” he says. “This is a paradigm shift in our thinking about how extensively people occupied these areas.”

For decades, archaeologists have visited the Upano Valley, a fertile basin at the foot of a massive volcano in the eastern foothills of the Andes, to excavate hundreds of human-made mounds left by pre-Hispanic peoples. But, until 2015, Upano had not yet been systematically imaged like other, similarly sized Mesoamerican settlements to the north.

Then, the Ecuadorian government scanned a 600-square-kilometer swathe of the valley. Based on his own expeditions in the valley over many years, archaeologist Stéphen Rostain of CNRS in Paris expected to see extensive infrastructure in the scans. But he was still surprised by the scale of what once existed when he and colleagues analyzed the lidar data.

Beneath the tree canopy was a massive network of roughly 6,000 mounds — once homes and community spaces — clustered into 15 settlements and connected by an intricate road system. The lidar data also revealed that the open spaces between settlements were in fact agricultural fields that had been drained to grow crops such as maize, beans, sweet potatoes and yucca. Within the settlements, the researchers found tiered gardens that would have kept some food closer at hand.

Put together, the results show that the valley wasn’t simply a series of small villages linked by roads, but “an entirely human-engineered landscape” built by skilled urban planners, Rostain says. Dating from several sites suggests the area was inhabited for roughly 2,000 years beginning around 500 B.C. by at least five different cultural groups. A next step will be to calculate how many people might have lived there.

“This landscape scale we’re able to document via airborne lidar really helps us understand what the variety of urbanism was in the past,” says Anna Cohen, an anthropological archaeologist at Utah State University in Logan who was not involved in the work. In particular, “it shows that you need to look at these green spaces in addition to the buildings.”

Beyond what the work says about the landscape, Fisher says, it’s also revealing a lot about the people who lived there. After Europeans’ conquest in predominately the 1500s, many Indigenous populations were almost wiped out by disease. “We see the Amazon today as a pristine tropical forest, but in reality, it’s an abandoned garden,” he says. “And this is the first time we’ve been able to see these people since they were victims of this incredible mortality event.”