Aerial surveys have revealed the largest pre-colonial cities in the Amazon yet discovered, linked by an extensive network of roads.
“The settlements are much bigger than others in the Amazon,” says Stéphen Rostain at the French National Center for Scientific Research in Paris. “They are comparable with Maya sites.”
What’s more, at between 3000 and 1500 years old, these cities are also older than other pre-Columbian ones discovered in the Amazon. Why the people who built them disappeared isn’t clear.
It is often assumed that the Amazon rainforest was largely untouched by humans before the Italian explorer Christopher Columbus reached the Americas in the 15th century. In fact, the first Europeans reported seeing many farms and towns in the region.
These reports, long dismissed, have in recent decades been backed up by discoveries of ancient earthworks and extensive dark soils created by farmers. One estimate puts the pre-Columbian population of the Amazon as high as 8 million.
Rostain and his colleagues have been studying archaeological sites in the Upano valley of the Ecuadorian Amazon, in the foothills of the Andes, since the 1990s. Traces of ancient settlements were first found there in the 1970s, but only a handful of sites have been excavated.
In 2015, Rostain’s team did an aerial survey with lidar, a laser scanning technique that can create a detailed 3D map of the surface beneath most vegetation, revealing features not normally visible to us. The findings, which have only now been published, show that the settlements were far more extensive than anyone realised.
The survey revealed more than 6000 raised earthen platforms within an area of 300 square kilometres. These are where wooden buildings once stood – excavations have revealed post holes and fireplaces on these structures.
Most platforms are around 10 by 20 metres and 2 metres high, and are thought to be the former sites of houses. The largest is 40 by 140 metres and 5 metres high, and was thought to be the site of monumental buildings used for ceremonies.
Around the platforms were fields, many of which were drained by small canals dug around them. “The valley was almost completely modified,” says Rostain.
Analysis of pottery suggests that maize, beans, manioc and sweet potatoes were grown.
Overall there were five major settlements in the area surveyed. They could be described as garden cities, says Rostain, due to their low density of buildings.
The survey also revealed a network of straight roads created by digging out soil and piling it on the sides. The longest extends for at least 25 kilometres, but might continue beyond the area that was surveyed.
What is peculiar is that the Upano people went to great lengths to make the roads straight, says Rostain. In places they dug down 5 metres rather than follow contours, for instance. So the roads probably had symbolic significance, as there was no practical reason to make them straight, he says.
In places there are also signs of defensive structures such as ditches, so there may have been some conflict between groups.
In the rest of the Amazon, many settlements were abandoned after the arrival of Europeans, probably because diseases and violence unleashed by the invaders killed a large proportion of the population.
All the Upano artefacts dated by Rostain’s team are older than 1500 years, however, suggesting the settlements in the valley were abandoned after this time, long before the colonial era. Why isn’t clear, but the team has found layers of volcanic ash, so it is possible a series of eruptions forced people to leave the valley.
“This shows an unprecedented degree of complexity and density of settlement for this early time frame,” says Michael Heckenberger at the University of Florida. “The authors justifiably conclude that the complexity and scale are comparable with better known cases, such as the Maya, at this time.”
“This is the largest complex with large settlements so far found in Amazonia,” says Charles Clement at the National Institute of Amazonian Research in Manaus, Brazil.
What’s more, it was found in a region of the Amazon that other researchers had concluded was sparsely inhabitated during pre-Columbian times, says Clement.