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To learn about the people and societies that existed long before us,
we often have to literally dig up the past.
Excavating historical sites is one of the major ways
archaeologists piece together human history.
But it’s not easy to find every interesting site, let alone excavate it.
The traces of many major civilizations are buried in hard-to-reach places.
That’s why scientists are now using lasers to scan the ground for structures
that might have been built by ancient people,
offering clues about where and how they lived.
One place archaeologists are especially interested in is the Amazon.
This region has been home to indigenous groups for thousands of years,
since long before the arrival of Spanish colonizers.
In the past, archaeologists assumed that these people lived in
small, isolated groups rather than larger societies.
In fact, many considered the region unsuitable for permanent settlement.
So researchers figured that the Amazon never had sophisticated societies that
might have transformed the environment through things like irrigation or agriculture.
That notion helped create an image of the Amazon as this pristine environment,
unaffected by humans until modern times.
But a growing amount of evidence suggests… that may be anything but the truth.
For instance, satellite images and archaeological expeditions in recent years
have revealed some human settlements in the southern Amazon.
But it was not clear how extensive they were.
Researchers also couldn’t tell if they were related to each other
or just self-contained sites.
But there was reason to believe they could be connected.
In historical accounts from the 1600s, Jesuit missionaries in this region described
large villages with what they called powerful chiefs and influential shamans.
So, archaeologists began to wonder if this could be true.
It’s well established that between 500 and 1400 CE,
a people known as the Casarabe lived in this region.
They inhabited a tropical savanna called Llanos de Moxos.
So, archaeologists became intrigued by the possibility that the Casarabe had
developed a sophisticated agricultural civilization in what’s now a tropical rainforest.
If they had, it would suggest that human civilization
may have left a footprint on the Amazon rainforest:
this place that was considered “untouched” before modern times.
But actually investigating this question was a challenge.
The Amazon is vast and full of rough terrain
that makes it hard to explore through ground expeditions.
And an aerial view won’t offer many clues because the tree cover is too dense.
So, in a 2022 study, researchers turned to a relatively new tool: lidar.
Lidar works by bouncing pulses of laser light off the ground from the air.
Since light travels at a fixed speed, lidar detectors can tell exactly how far away
the ground is based on how long it takes the laser pulse to bounce back.
So, by scanning an area with lidar,
researchers can actually construct 3D maps of the surface.
Lidar can’t pass through trees, but enough pulses will make it through gaps
in foliage that this technology can be used to map out forest floors.
So the researchers in this study decided to use lidar to look for
possible human-made structures beneath the trees in Llanos de Moxos.
They launched lidar pulses from a helicopter down into the Amazon.
And what they found was incredible.
In all, they identified 26 sites with structures
that appeared to have been built by the Casarabe people.
These structures were organized into what the researchers described as an
urban-like system: essentially, a group of cities and smaller settlements.
These weren’t cities like New York or Chicago,
where many people live together in a tightly packed area.
They were more like large population centers surrounded by collections of settlements.
These centers were protected by curved moats and defensive walls, and they
were connected to the smaller surrounding settlements by raised causeways.
Kind of like how today’s cities are linked to smaller towns.
This design suggests that some people would have lived
out around their farms or hunting grounds,
but they would have been well connected to the population centers.
Another thing that stood out about these urban systems
was how well they managed water.
At the time the Casarabe lived, the region wasn’t covered in trees yet.
Instead, it flooded seasonally, and went through cycles of droughts and floods.
So it took some engineering to have a steady supply of water that could support
a major civilization.
But the Casarabe were up to the task.
In the lidar images, researchers found large reservoirs.
And around one of the population centers,
they found canals connecting it with rivers and a lake.
All this evidence indicated that ancient people hadn’t just lived passively in the rainforest.
They had redirected water and reshaped the land,
transforming this tropical region into an agricultural landscape.
This finding settles the debate about whether or not people developed settlements
in the southern Amazon before the arrival of Europeans.
In fact, not only did the Casarabe settle there, they developed a civilization
far more sophisticated than anyone expected to find in this region.
Finding this type of urbanism in the Amazon, of all places, highlights the fact
that rainforests are not always pristine, untouched environments.
In fact, the Amazon may not be the only rainforest to have hosted an ancient civilization.
It’s possible that other dense rainforests, like the Congo Basin in central Africa,
could have seen urban development in the past too.
And as lidar gains strength as an archaeological tool,
scientists are in a better place to get to the bottom of these questions.
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