Some historic sites in Cambodia can be seen with the naked eyes. Others require lidar, a laser-based technology. (Courtesy of Damian Evans/Journal of Archaeological Science)

Cities buried beneath the jungle ground — it sounds like something out of an Indiana Jones film.

Yet Australian archaeologist Damian Evans has spent the past several years searching for them in the dense jungleland near Angkor Wat in Cambodia. During a phone interview early Monday morning, Evans told The Washington Post he and his team have mapped out more than 734 square miles of land, including “basically every modern temple complex in the entire country to some degree.” The findings offer new insight not only into the Khmer Empire, which reigned in what is now called Cambodia from around the 9th to the 15th centuries, but into the populations that lived in the area long before then.

Most dramatic among the findings is an entire medieval city for which Evans and his team had searched for almost 10 years before concluding it didn’t exist.

Evans also said this mapping proves, maybe for the first time, that human beings have terraformed the earth by diverting rivers and cutting down forests for thousands of years, since well before we had written records.

“The broad conclusion to draw from this is that we’ve underestimated how much humans have shaped their environments,” Evans said.

They’ll be presenting the findings in a paper set for release in the Journal of Archaeological Science and in a presentation Monday at the Royal Geographic Society in London.

The technology that made this possible would have made Indiana Jones’s job a lot easier, albeit less swashbuckling. Previously, archaeologists would have been forced to do this sort of topological mapping on foot, a slow and burdensome process, particularly in dense jungles like those of Cambodia. But advancements made in lidar — which stands for light detection and ranging — have made it possible to perform this sort of research from the air.

The technology was actually created in the 1960s, just after the laser was invented. It works a little like radar, which uses radio waves to find foreign objects. To put it simplistically, if a wave bounces back, then you know something is there. Lidar does the same, only it uses pulses of light, or lasers, to detect objects. It’s the same technology police use when hunting down speeding cars on the interstate.

But at its inception, lidar could only shoot about 2,000 pulses per second, which rendered it fairly useless for the sort of work Evans and his team do. At those levels, most of the pulses would merely bounce off treetops and the dense blanket of leaves under them, offering little to no insight as to what lay below. Modern lidar, though, can fire up to 600,000 shots per second. At that rate, enough lasers make it through the vegetation to offer information on what is underneath.


The yellow section was mapped in 2012 using lidar. The red part was mapped last year. (Courtesy of Damian Evans/Journal of Archaeological Science)

What is underneath is often enough to draw conclusions as to what was once there. Much of the Khmer world was built with biodegradable materials like wood and thatch that have long decayed, according to the paper, but topography points to what structures once existed. Wooden houses, for example, were built on mounds of earth designed to keep them above water during flood season, and lidar will detect those mounds.

Evans said mapping the topology by helicopter using the technology is just as effective as performing the work by hand — and far, far quicker.

“There was a French team that had been working in the central Angkor areas and they covered nine square kilometers the old-fashioned way,” Evans said, meaning they used machetes to cut through the vegetation and shovels to reach the trace materials that indicated where a canal or a roadway might have been. It took that team many years to map those nine kilometers, which Evans said his team was able to do with the same accuracy in a mere one to two hours using lidar.

He also said that given how quickly urbanization is taking place in Cambodia and elsewhere, it’s likely this large-scale mapping might never have occurred without the technology. Modern urbanization may have destroyed the topography.

In 2013, he wrote, “Now, for the first time in my 16-year career, there is no ‘next big thing’ — lidar is it. We have arrived.”

He continued:

The fact is that the transformative power of lidar lies quite simply in its unparalleled ability to “see through” the vegetation that has previously obscured the traces of early civilizations that remain etched into the surface of the landscape. In many places, what we had before was a collection of temples that were just dots on a map, because the wooden cities that once surrounded them decayed centuries ago. Now what we have are entire urban landscapes mapped in elaborate detail. Imagine having a map of a European city consisting only of the locations of churches, compared to having a complete street map of the same city, and you get an idea of what an extraordinary leap forward this is for those of us interested in the history of lived-in spaces.

That leap forward for Evans came last March and April, while Evans was leading the Cambodian Archaeological Lidar Initiative, which was funded by a 1.5 million euro grant from the European Research Council, according to a press release.

The results are expansive, and not all are published in the journal article. In fact, the press release states, “The coming weeks and months will see the publication of a number of reports, articles and peer-reviewed publications deriving from the 2015 archaeological lidar campaign in Cambodia.”

Perhaps the most striking thing to happen is the discovery of a city no one could find at Preah Khan of Kompong Svay, a large religious complex about 60 miles east of Angkor. Evans and his team sought the city for 10 years, finally concluding that it didn’t exist. Until one day, as if someone had turned on a flashlight in a dark room, it appeared on the computer screen, after being mapped by lidar.

“We had spent a decade on the ground … looking for a city that we figured must be around somewhere … surrounding this temple,” Evans said. “All of a sudden, the city has more or less instantly appeared on the screen in front of us. It had been hiding in plain sight. A city that we figured wasn’t there just appeared.”

Added Evans, “Usually the reactions from the people in the room are not printable in a newspaper, but it’s quite a thing to behold.”

This isn’t the first time Evans himself has used lidar to map a city that was mostly covered in dense vegetation. In 2012, he and his team used it to map parts of Mahendraparvata, which many — to Evans’s chagrin — called a “lost city.” He explained in The Diplomat that it was never “lost” — indeed, “a century or more of prior scholarship” hinted that it was there — but it was also unseen.

Now, it’s not just seen; it’s almost entirely mapped. This new survey, which focused on a much larger area, found the full expanses of Mahendraparvata to be potentially even larger than Phnom Penh, the capital of and largest city in Cambodia.

Among the findings were unexplained geographic landmarks throughout the country, previously thought to be unique to Angkor Wat (courtesy Damian Evans / Journal of Archaeological Science) Among the findings were unexplained geographic landmarks throughout the country, previously thought to be unique to Angkor Wat (Courtesy of Damian Evans/Journal of Archaeological Science)

Though much of the data is currently fairly raw, scholars will be able to study it and draw insight and conclusions from the topography. Some already have.

For example, Evans told The Guardian, “Our coverage of the post-Angkorian capitals also provides some fascinating new insights on the ‘collapse’ of Angkor. There’s an idea that somehow the Thais invaded and everyone fled down south — that didn’t happen, there are no cities [revealed by the aerial survey] that they fled to. It calls into question the whole notion of an Angkorian collapse.”

In a broader scale, the data could teach us about the advent of some human technology. For example, elaborate water management systems — the usage of dams to divert rivers and the construction of waterways as a means of irrigation — in the area were previously thought to be confined mainly to Angkor, which means the practice of using them would have started in the 9th century. But, according to the journal article, it might have been a “common characteristic” of the area dating back to around the 5th century. As the paper stated, “this is usually thought to be an Angkor period innovation, but here we have an example of a very sophisticated urban water management system potentially dating from several hundred years earlier.”

Finally, the study found “unexplained, geometric linear patterns” across Cambodia that were also previously thought to be unique to Angkor Wat.

“We still don’t really understand what they are,” Evans told the Guardian. “They could have been gardens of some kind. But they’re very obviously associated with temples of a particular period.”

Many conclusions will be drawn from the data in the coming months, but some experts are thrilled simply to have it.

“I have been to all the sites described and at a stroke, they spring into life … it is as if a bright light has been switched on to illuminate the previous dark veil that covered these great sites,” Charles Higham, research professor at the University of Otago in Dunedin, New Zealand, told the Guardian. “Personally, it is wonderful to be alive as these new discoveries are being made. Emotionally, I am stunned. Intellectually, I am stimulated.”

The full study can be found in the August edition of the Journal of Archaeological Science.