Great mysteries of archaeology: an ancient Amazonian world revealed from the sky
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Rainforest of secrets.<br>BIOSPHOTO/Alamy
https://theconversation.com/great-mysteries-of-archaeology-an-ancient-amazonian-world-revealed-from-the-sky-282006
https://theconversation.com/great-mysteries-of-archaeology-an-ancient-amazonian-world-revealed-from-the-sky-282006
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From the air, you see it only through the constant jolt, tilt and shudder of the low-flying Cessna aircraft. The landscape of the Llanos de Moxos, northern Bolivia, appears as a disconnected patchwork of open grassland savannahs, forest islands and lakes.
It feels random, almost unreadable. Only gradually does the pattern resolve itself: raised causeways or paths fanning out to link the forest islands, and a dense, scattered web of canals threading the terrain. Slowly you realise it’s a structured network of intersecting lines, enclosures and roads – the imprint of past human design.
Aerial view of Llanos de Moxos.<br>Jose Iriarte, CC BY-SA
If you stand on the open savannah, there is almost nothing to see of this ancient network. The horizon feels open, with fires in the distance from local people burning pastures and clearing forest as dry season begins. The old geometry is still faintly perceptible, but you have to know how to look.
Step into the patches of forest and the canopy closes in. The earth softens underfoot and mosquitoes descend in relentless swarms. The sweat on your neck thickens into a humid film, carrying the familiar scent of suncream and the sharper, chemical note of DEET.
In the uneven light between the trees, the landscape dissolves into subtle rises and depressions. Against the rhythmic swish of machetes as our guides cut through the vegetation, your mind tries to piece together the fragments of structures into something coherent. Flying overhead doesn’t reveal anything about this forest area in the way that it does with the savannah. But fortunately recent advances in technology have transformed what we are able to see.
Surveying in the dense Amazon rainforest.<br>Jose Iriarte, CC BY-SA
Archaeological explorations in this part of the world have been completely changed by lidar in the past couple of decades. Lidar maps an area from a plane or drone by bouncing rapid laser pulses off the Earth’s surface. Some of these pulses penetrate the forest canopy, reach the ground and reflect back to the sensor.
By measuring the return time, the system can generate highly precise three-dimensional models of the terrain. This allows you to strip away the camouflage of vegetation, making it possible to see what lies below the Amazonian forest for the first time.
It reveals the ancient Llanos de Moxos as not simply a collection of settlements, but an entire urbanised landscape. A large part in the south-east of this region belonged to the Casarabe culture, which dominated between around AD500 and 1400. It extends across 20,000km², which is roughly the size of New Jersey in the US.
The Casarabe organised into a hierarchy of four different sizes of settlements (those forest islands mentioned above). The biggest ones – the primary settlements – were as large as 3km² or 300 hectares. That’s enough space for over 400 football pitches, suggesting that they could have accommodated substantial numbers of people.
Welcome to our series on the great mysteries of archaeology. Viking explorers, Amazonian cities, artefacts from before civilisation. Archaeology may be all about the past, but it’s constantly shifting with every scientific discovery. This series will dig into some of the most fascinating debates in the field today.
These settlements connect along the raised causeways to smaller secondary and tertiary sites a number of kilometres away, all of which were permanently inhabited as opposed to empty ceremonial hubs. A fourth tier consists of groups of isolated mounds located out in the pampas, which likely correspond to dwelling areas occupied by farmers who would have worked the fields.
It’s not possible to show a lidar image of these four different types of sites interconnecting because they are too far apart for the resolution available, but the image below of a primary settlement known as Loma Cotoca shows the kinds of things we are now documenting.
Lidar shot of Loma Cotoca.<br>Jose Iriarte, CC BY-SA
It features some very impressive civic-ceremonial architecture: conical pyramids over 20 metres tall and U-shaped structures that may have acted as areas for public gatherings for speeches or ceremonies. These were built on top of man-made platforms rising as much as five metres off the ground and extending over 20 hectares. To be clear, this is all still hiding under the forest, but the lidar data reveals the shape, height and layout of what lies below.
The volume of earth moved to create this...