Lost cities #7: how Nasa technology uncovered the ‘megacity’ of Angkor

Recent laser surveys have revealed traces of a vast urban settlement, comparable in size to Los Angeles, around the temples of Angkor in the Cambodian jungle. The ancient Khmer capital was never lost … it just got a bit overgrown

Clusters of gigantic stone pine cones poke above the dense forest canopy in Cambodia, looking like ancient rocket ships poised for take-off, their distinctive silhouettes reflected in the mirror-calm moat below. Tree root tentacles roam along crumbling cornices, winding their way around door frames and strangling the serene stone faces of smiling god-kings, oblivious to the fact that their empire has long succumbed to the natural world.

 

When you’re exploring the enigmatic temples of Angkor, along with the two million other tourists who come here each year, it can still feel like you’re uncovering this lost kingdom for the first time. What’s harder to imagine as you roam between the ruined sites, each set apart in the depths of the jungle, is that these monuments were once part of the largest, most sprawling city on the planet.

 

It’s a hunch that archaeologists have had for decades, but which was only recently confirmed in astonishing detail by an aerial laser survey, which cut through the foliage for the first time a few years ago to reveal the grid of a vast urban settlement stretching for miles around the moated compounds. It showed that the ancient Khmer capital, which flourished from the ninth to 15th centuries, had more in common with Los Angeles than this series of temples standing in splendid isolation in the jungle might suggest.

 

“The laser technology has been a total game-changer,” says Damian Evans, the Australian archaeologist who has been leading the airborne scanning survey at the École Française d’Extrême-Orient, working with Cambodian APSARA National Authority and the Ministry of Culture and Fine Arts. “Our surveys have revealed the pattern of a settlement comparable in size to LA or Sydney, with an urban form that resembles the kind of dispersed low-density megacity characteristic of the modern world.”

 

For centuries, explorations of Angkor had been preoccupied with the temple compounds themselves, focusing on the religious symbolism of the structures and the cosmological worlds depicted in their intricate bas reliefs. And it’s not hard to see why.

 

“Grander than anything left to us by Greece or Rome,” was the judgment of young French explorer Henri Mouhot, when he first stumbled across Angkor Wat in 1858, a complex he described as “a rival to [the temple] of Solomon, erected by some ancient Michelangelo”. This central temple alone, built by King Suryavarman II in the early 12th century, remains the largest religious complex in the world, four times larger than Vatican City, its five conical towers rising above a 160-hectare precinct.

 

As the only surviving structures in the area, it was assumed that the temples must have operated like medieval walled towns, each inhabited by staff of a few thousand people. Perhaps they had been built by successive kings, as the royal family and their retinue moved from one complex to the next, leaving a series of separate cities dotted across the plain, each bordered by a defensive moat.

 

The reality, it turns out, was nothing of the sort. The laser surveys, conducted in 2012 and 2015, revealed that these sacred walled precincts didn’t contain much at all. They were instead surrounded by a sprawling urban network, a grid of boulevards, streets and canals that extended far into the surrounding landscape, covering an area larger than modern-day Paris. What archaeologists had been studying for generations was simply the equivalent of a European city with everything wiped away except for the churches and cathedrals.

 

At its peak in the 12th century, when London had a population of 18,000, Angkor was home to hundreds of thousands, some estimate up to three-quarters of a million people. So what form did this megacity in the rice fields take?

 

“I’m reluctant to use the word ‘city’,” says Evans. “Angkor doesn’t follow the usual pattern of an ancient walled city with a clearly defined edge. Instead, we discovered a very densely populated downtown urban core, covering an area of 35-40 sq km, which gradually gives way to a kind of agro-urban hinterland. It slowly dissolves into a world of neighbourhood shrines, mixed up with rice fields, market gardens and ponds.” It was the prototype of modern-day suburban sprawl.

 

Thanks to technology developed by Nasa, all of this could be gleaned from a few hours of helicopter flight, as opposed to generations of hacking through the undergrowth with machetes (while keeping a lookout for landmines). Shooting a million laser beams every four seconds from the bottom of a helicopter, the lidar technology (which stands for light imaging detection and ranging) allows a kind of virtual deforestation to take place, stripping away the tree canopy to reveal what lies beneath on the forest floor.

 

The findings were a revelation. The scanning exposed a topography inscribed with a precise network of furrows and mounds, the bones of the city etched into the landscape.

 

“On the ground you just see lumps and bumps,” says Evans, “but this aerial view shows a very sophisticated system of road networks, planned neighbourhoods and intricate waterworks. Angkor was a work of geoengineering on an unparalleled scale.”

 

Any evidence of these neighbourhoods on the ground has long since rotted away. In Khmer society, stone was reserved exclusively for religious monuments, built of great blocks floated here from quarries 30 miles away along specially dug canals (as the wider laser survey revealed last year). Everything else – even the royal palaces – was made of wood and thatch, with homes raised up on stilts on top of earthen mounds, designed to keep them above the floodwaters in the rainy season

 

The Khmer’s mastery over the natural landscape was perhaps their greatest achievement, and the lidar mapping has exposed complex levels of terraforming and water management systems that were way ahead of any other settlement of the era.

 

Once again, earlier archaeological studies focused on the symbolic role of water in Angkor’s cosmological order, reading the vast reservoirs as symbols of the mythological oceans surrounding Mount Meru, home of the Hindu gods. While the watercourses evidently played a part in the sacred geography of the city, they were fundamentally there to irrigate the rice fields, the source of the empire’s great wealth. Success in a tropical climate ultimately depended on the ability to mitigate flooding during the summer monsoon and store enough water to irrigate the fields during dry season – something the Khmer rulers had clearly mastered.

 

Residential neighbourhoods were arranged around thousands of communal rainfall ponds, while the fields were irrigated by a pair of great reservoirs, or “barays”, the whole system connected by an extensive network of canals and channels. The West Baray, which stretches five miles by one mile to the west of downtown Angkor, remains the largest hand-cut body of water on earth. Contained by tall earthen dikes, it stands as the pinnacle of the Khmer ability to harness the landscape for its own ends.

 

But this hydrological virtuosity, Evans and his team now believe, might also have been at the root of Angkor’s undoing, shedding new light on the ultimate reason for this magnificent city’s decline.

 

Archaeologists have long speculated on why the Khmer capital descended into ruin. One theory is that the city was sacked by a Siamese invasion in 1431, prompting the kings and their people to flee en masse to an area near present-day Phnom Penh. But there is little evidence of the kind of settlements indicative of a mass migration.

 

Others argue that the transition from Hinduism to more placid Buddhism, following the reign of Jayavarman VII, sapped the Angkorian civilisation of its war mongering, monument-building vitality. Yet that conveniently ignores the violent expansions of other Buddhist rulers elsewhere in the world at the time. Another tenuous suggestion is that the Khmer exhausted themselves with all the building projects and finally collapsed from monument fatigue.

 

Evans, however, now believes that environmental factors played a significant part. “Looking at the sedimentary records, there is evidence of catastrophic flooding,” he says. “In the expansion of Angkor, they had devastated all of the forests in the watershed, and we have detected failures in the water system, revealing that various parts of the network simply broke down.” With the entire feudal hierarchy reliant on the successful management of water, a break in the chain could have been enough to prompt a gradual decline.

 

While it might be tempting to dwell on the colourful vision of a mass exodus, Evans is keen to emphasise that there was no dramatic collapse at all. “There is a lot of evidence for continued vitality in Angkor,” he says. When Portuguese traders visited in the 16th century, and French explorers came here in the 19th century, they encountered communities of several thousand people living in and around the temples. “It might have disappeared from the consciousness of Europeans for a time,” he adds, “but Angkor was never a ‘lost city’.” It just got a bit overgrown.