
In the autumn of 1929, Anne Morrow Lindbergh and her
husband Charles flew across the Yucatán Peninsula. With Charles at the
controls, Anne snapped photographs of the jungles just below.
She wrote in her journal of Maya structures obscured
by large humps of vegetation. A bright stone wall peeked through the leaves,
"unspeakably alone and majestic and desolate - the mark of a great
civilization gone."
Nearly a century later, surveyors once again took
flight over the ancient Maya empire, and mapped the Guatemala forests with
lasers.
The 2016 survey, whose first results were published
this week in the journal Science, comprises a dozen plots covering 830 square
miles, an area larger than the island of Maui. It is the largest such survey of
the Maya region, ever.
The study authors describe the results as a
revelation. "It's like putting glasses on when your eyesight is
blurry," said study author Mary Jane Acuña, director of El Tintal
Archaeological Project in Guatemala.
In the past, archaeologists had argued that small,
disconnected city-states dotted the Maya lowlands, though that conception is
falling out of favor.
This study shows that the Maya could extensively
"exploit and manipulate" their environment and geography, Acuña said.
Maya agriculture sustained large populations, who in turn forged relationships
across the region.
Combing through the scans, Acuña and her colleagues,
an international 18-strong scientific team, tallied 61,480 structures. These
included: 60 miles of causeways, roads and canals that connected cities; large maize
farms; houses large and small; and, surprisingly, defensive fortifications that
suggest the Maya came under attack from the west of Central America.
"We were all humbled," said Tulane
University anthropologist Marcello Canuto, the study's lead author.
"All of us saw things we had walked over and we
realized, oh wow, we totally missed that."
Preliminary images from the survey went public in
February, to the delight of archaeologists like Sarah Parcak. Parcak, who was
not involved with the research, wrote on Twitter, "Hey all: you realize
that researchers just used lasers to find *60,000* new sites in Guatemala?!?
This is HOLY [expletive] territory."

Parcak, whose space archaeology program
GlobalXplorer.org has been described as the love child of Google Earth and
Indiana Jones, is a champion of using satellite data to remotely observe sites
in Egypt and elsewhere.
"The scale of information that we're able to
collect now is unprecedented," Parcak said, adding that this survey is
"going to upend long-held theories about ancient Maya society."
With support from a Guatemala-based heritage
foundation called Pacunam, the researchers conducted the massive and expensive
survey using lidar, or light detection and ranging. They mapped several active
archaeological sites, plus well-studied Maya cities like Tikal and Uaxactun.
Lidar's principles are similar to radar, except
instead of radio waves lidar relies on laser light. From an aircraft flying
just a few thousand feet above the canopy, the surveyors prickled each square
meter with 15 laser pulses. Those pulses penetrate vegetation but bounce back
from hard stone surfaces. Using lidar, you can't see the forest through the
invisible trees.
Beneath the thick jungle, ruins appeared. Lots and
lots of them.
Extrapolated over the 36,700 square miles, which
encompasses the total Maya lowland region, the authors estimate the Maya built
as many as 2.7 million structures. These would have supported 7 million to 11
million people during the Classic Period of Maya civilization, around the years
650 to 800, in line with other Maya population estimates.
"We've been working in this area for over a
century," Canuto said. "It's not terra incognita, but we didn't have
a good appreciation for what was really there."
Archaeologist Arlen Chase, a Maya specialist at the
University of Nevada at Las Vegas who was not involved with this survey, said
for years he has argued that the Maya society was more complex than widely
accepted.
In 1998, he and archaeologist Diane Chase, his wife,
described elaborate agricultural terraces at the Maya city of Caracol in
Belize. "Everybody would not believe we had terraces!" he said.
He gets much less push back now, he said. "The
paradigm shift that we've predicted was happening is in fact happening"
Chase said, which he credits to lidar data. He has seen lidar evolve from a
"hush-hush type of technology" used by the military to map Fallujah
streets to a powerful archaeological tool.
Chase, who previously used lidar at Caracol, where as
many as 100,000 people lived, compares this technology to carbon-14 dating.
Radiocarbon dating gives archaeologists a much more accurate timeline.
Lidar is about to do the same for archaeologists'
sense of space, particularly in densely forested areas near the equator. Two
years ago, researchers used lidar mapped dense urban infrastructure around
Angkor, the seat of the medieval Khmer Empire in Cambodia.
"We're just getting started in so many major
sites around the world, whether it's Angkor Wat, whether it's Tikal in Central
America or major sites in Egypt," Parcak said.
For all its power, lidar cannot supplant
old-fashioned archaeology. For 8 percent of the survey area, the archaeologists
confirmed the lidar data with boots-on-the-ground visits.
This "ground truthing" suggests that the
lidar analysis was conservative - they found the predicted structures, and then
some.
"There is still much more ground to cover and
work to do," said Acuña, who will continue to study the large ancient Maya
city of El Tindal.
Could you imagine, Canuto said, what might be found
through a lidar survey of the Amazon? With technology like this, no forested
frontiers are final.
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