Beneath the Surface

Question: What technological breakthrough is reshaping everything we thought we knew about archaeological sites like Angkor Wat?

Answer: LiDAR

Some archaeologists say that LiDAR technology is producing findings so revolutionary that it is “rewriting history.” It is doing just that in Angkor Wat, Cambodia. Scholars had long speculated that there had to be more to the Khmer Empire than Angkor, the massive but isolated religious sanctuary near Siem Reap. Recent LiDAR scans have shown that not only was the Khmer capital much larger than previously thought, but the Khmer Empire was the largest on Earth during its 12th-century peak.

Before the details, let’s explain what LiDAR is and why it’s such a game-changer in the archaeological world.

LiDAR—uncovering civilizations that have been hiding in plain sight

LiDAR is short for Light Detection and Ranging (as opposed to RADAR, which is short for Radio Detection and Ranging). It’s a laser technology that sends out about 150,000 laser pulses per second from an airplane, helicopter, or any elevated platform to the ground below. When aimed at a dense jungle (like in Cambodia), most of the beams hit the treetops and bounce back, but many slip through openings in the canopy and reflect off the actual ground level. Once computer algorithms do their thing, what you’re basically left with is an X-ray of every bump, depression, and man-made structure that has been hiding in plain sight under the dense undergrowth for centuries.

The vertical precision of LiDAR technology is within four inches, which means it can detect subtle topographical features like ancient farming terraces or early fortifications. And most importantly, LiDAR can cover an area of about 50 square miles in just one day—to do this on foot by ground teams would take years. In fact, LiDAR is uncovering lost civilizations hidden beneath dense rainforests and impenetrable jungle canopies faster than research teams can even get there to examine them.

The LiDAR mapping projects in Cambodia exposed close to 400 square miles of concealed infrastructure surrounding the Angkor temple complex and one-time capital of the Khmer Empire. LiDAR also revealed an elaborate water control system and roadways that connected dozens of temple locations. The discoveries have shown that rather than an isolated religious sanctuary, Angkor was, in fact, the largest preindustrial urban complex in the world.

The same LiDAR that revealed the vast scale of Angkor may have also solved the great mystery of the empire’s collapse. Scholars have long believed that the Khmer Empire fell in 1431 after its capital was sacked by an invading Thai army, which caused the population to abandon Angkor and move closer to Phnom Penh, Cambodia’s current capital. But the research gleaned from the LiDAR scans has revealed that this wasn’t the case. The empire’s collapse wasn’t because it was conquered, but due to a failure of its sophisticated hydraulic system—which extended over hundreds of miles and appears to have been built some two centuries before the technology behind them was believed to have existed. The studies have shown that a combination of prolonged droughts interrupted by intense monsoon seasons in the early 15th century caused the system to fail. Once this happened, there was a gradual loss of the local population in the affected areas of the megalopolis.

LiDAR breakthroughs as fresh as today’s headlines

As if to drive home the game-changing nature of LiDAR, a featured article in this week’s Boston Globe reports on a LiDAR discovery that is completely reshaping our understanding of the history of the Amazon. Archaeologists flying over the southwestern Amazon (near the borders of Brazil, Peru, and Bolivia) have just discovered hundreds of ancient geoglyphs (meaning “earth markings”), including giant circles, squares, and other geometric figures. Located deep beneath the forest canopy and spanning hundreds of miles, the geoglyphs date from between 600 BC and 850 AD. All indications point to a complex society living in the Amazon Basin a full millennium before the Spanish and Portuguese colonists arrived.

Although this region of the Amazon has always been depicted as an “untouched wilderness,” a chronicle from a missionary who traveled extensively here in the 1540s spoke of a land “thickly populated” with “many large settlements” including some that “stretched for five leagues without any space from house to house.” But those accounts were widely dismissed in the centuries that followed. Scientists back then also struggled to accept that a large complex society could develop in the Amazon without European-style agriculture. Perhaps it was easier to cling to the false idea that the region was a pristine rainforest than acknowledge that an indigenous population was almost wiped out by disease and colonization. But it looks like the Amazon’s ancient past is about to get a complete do-over—and it’s all thanks to LiDAR.

If there is one thing that can be stated with near certainty, technological advances like LiDAR are challenging everything that historians believe about ancient civilizations. As advancements in the field progress, we can anticipate even more groundbreaking discoveries to enhance our understanding of both the distant and not-so-distant past.

A few more groundbreaking discoveries using LiDAR 

• My oh Maya—Perhaps LiDAR’s greatest contributions of late have been in northern Guatemala, where a recent aerial survey penetrated the dense jungle and uncovered a sprawling Maya site—including more than 60,000 previously unknown structures in Guatemala’s Maya Biosphere Reserve alone. The new findings shatter previous population estimates of the Maya, with current research suggesting that 10-15 million people populated this region during the civilization’s zenith—roughly twice the number scholars had previously calculated.
• Mucho Machu Picchu—Recent LiDAR surveys have uncovered a wealth of hidden terraces and structures beneath the thick jungle canopy surrounding Machu Picchu, findings that suggest the site was much more expansive than previously believed.
• AI, AI, Ohhh—Rather than LiDAR, it was Artificial Intelligence (AI), with a little help from drone technology, that is greatly increasing our understanding of Peru’s Nazca Lines. The collection of giant patterns and pictures etched into the arid plains of southern Peru has mystified archaeologists for centuries. It took close to a hundred years with traditional ground and aerial surveys to identify about 430 of these designs created between 200 BC and 650 AD. An AI model recently discovered 303 new geoglyphs, almost doubling the number, in just six months.
• Squaring the circle—Our understanding of the mysterious stone circle of Stonehenge has increased with the discovery of many new burial mounds, enclosures, and pathways uncovered by recent LiDAR surveys of its surroundings, suggesting the site was part of a much larger and more complex ceremonial landscape.
• An even greater Great Wall—Laser technology has discovered wide swathes of previously unknown sections of the Great Wall of China hidden beneath centuries of vegetation, providing new insights into the wall’s construction phases.
• A titanic effort—Recent LiDAR scans have produced the most detailed 3D models to date of the Titanic, in its final resting spot two miles beneath the North Atlantic. The models provide invaluable insights into the ship’s current condition and the events that led to its sinking.
• Roman life in ruins—Detailed topographical maps of the ancient city of Pompeii, buried by the eruption of Mount Vesuvius in 79 AD, produced by LiDAR technology have revealed countless previously unnoticed structures. The discoveries are providing archaeologists with exciting new perspectives on the Roman city’s layout and what daily life was like before disaster struck.

Behold the Angkor temple complex and imagine the grandeur of the Khmer Empire during Ancient Kingdoms: Thailand, Laos, Cambodia & Vietnam.