Angkor -- Medieval 'Hydraulic City' -- Unwittingly Engineered Its Environmental Collapse

Angkor at sunset. (Credit: Image courtesy of University Of New South Wales)

September 5, 2007
University Of New South Wales (Australia)

Science Daily — The architects of Cambodia’s famed Angkor – the world's most extensive medieval "hydraulic city" – unwittingly engineered its environmental collapse, says research by UNSW scientists and a team of international scholars.

This revelation, published in the Proceedings of the National Academy of Science, supports a disputed hypothesis by French archaeologist Bernard-Philippe Groslier, who 50 years ago suggested that the vast medieval settlement of Angkor was defined, sustained, and ultimately overwhelmed by over-exploitation and the environmental impacts of a complex water-management network.

A succession of monarchs ruled the Angkor area from about 800 AD, producing the architectural masterpieces and sculpture now preserved as a World Heritage site. By the 13th century the civilisation was in decline, and most of Angkor was abandoned by the early 15th century, apart from Angkor Wat, the main temple, which remained a Buddhist shrine.

Groslier surmised that a network of roads, canals and irrigation ponds established between the 9th and 16th centuries proved too vast to manage. He argued that extensive land clearing for rice fields supporting up to a million people living beyond Angkor's walled city produced serious ecological problems, including deforestation, topsoil degradation and erosion.

Latter-day archaeologists disputed Groslier’s view because he was unable to support his hypothesis with empirical data about the landscape beyond Angkor's central temple complex.

Using modern day aerial photography and high-resolution ground-sensing radar, the international research team, including UNSW’s Professor Tony Milne, studied an area of nearly 3000 square kilometres, confirming Groslier's hypothesis by correlating their images to existing maps, topographic data sets and supporting information from extensive ground-based archaeological investigations.

The team discovered more than 1000 man-made ponds and at least 74 more temple sites in the Angkor region, revealing ruins covering an area of 1000 square kilometres.

The study's radar images were acquired from NASA via an airborne imaging radar (AIRSAR) data instrument capable of accurately reconstructing surface structures through cloud cover.

"The instrument can produce high-resolution images detecting surface structures as small as 20 cms in height and distinguish very subtle differences in surface vegetation and soil moisture,” says Professor Milne from the School of Biological, Earth and Environmental Sciences.

"This was of particular use in uncovering the archaeological landscape at Angkor. The distinctive spatial patterning of features manifests itself primarily in slight variations in topographic relief. This also influences the amplitude or 'brightness' of the radar signal returned to the sensor.”

“Both the topographic relief and the surface brightness can be helpful in identifying the possible location of former roads, canals and rice fields,” says Professor Milne. "When excavations were carried out, they prove to be the site of a canal or temple moat”.

Note: This story has been adapted from a news release issued by University Of New South Wales.

Metropolis: Angkor, the world's first mega-city

The discovery that the famous Cambodian temple complex sits in the midst of a vast settlement the size of London, which flourished until the 15th century, has astounded archaeologists - but also baffled them: why did it disappear?

15 August 2007
By Kathy Marks
The Independent (UK)

The huge sandstone temples of Angkor, built nearly 1,000 years ago and unearthed from the Cambodian jungle in the last century, are considered one of man's most outstanding architectural achievements. Last year more than a million tourists wandered through the ruins and watched the sun rise over the main temple's distinctive towering spires.

But, magnificent though the temple complex may be, it tells only part of the story of Angkor: a thriving metropolis, the world's first mega-city so mysteriously abandoned in the 15th century, and the former capital of the vast Khmer empire.

An international team of archaeologists has ascertained that the temple environs were just the core of a sprawling urban settlement that covered 700 square miles - a similar size to Greater London. They have spent 15 years mapping the area and putting together a picture of life in what is now established to have been the world's largest medieval city.

The "lost city of Angkor" was painstakingly uncovered by French archaeologists who spent much of the last century rescuing it from the forest and restoring it. Not surprisingly, they concentrated their efforts on the massive temples, which were built between the ninth and 13th centuries as monuments to the power and wealth of the Khmer kings. The rest of the region remained carpeted with vegetation, with few remnants of the ancient civilisation visible to the human eye at ground level.

A French, Cambodian and Australian team used aerial photographs, satellite imagery and high-resolution ground-sensing radar, provided by Nasa, to investigate what lay beneath the green cloak. What they found was the remains of 74 temples, as well as the sites of thousands of houses, roads, embankments, canals and ponds - all believed to have been part of an extensive, interconnected residential complex that included a large system of waterways. The team has just published its findings, together with a detailed map, in Proceedings of the National Academy of Sciences, a US journal.

Damian Evans, an Australian archaeologist who is deputy director of the Greater Angkor Project, said yesterday: "People never really considered Angkor as being much more than a scattering of temples in the landscape. In fact, it would have been a huge and popular city, full of life."

He and his colleagues report in their paper that, "even on a conservative estimate, greater Angkor at its peak was the world's most extensive pre-industrial low-density urban complex" - far larger than the ancient Mayan cities of central America, for instance, which covered 100 square miles at most. Mr Evans, who is based at the University of Sydney's archaeological computing library, said the Khmers of 1,000 years ago appear to have lived very similar lives to modern-day Cambodians. "They lived in clusters of houses on raised mounds to keep above the floodwaters in the wet season," he added.

"The mounds were in clusters, and scattered through them were these small village ponds. Between the houses were rice fields. And the core of this system was the village temple, in much the same way that Buddhist temples are the core of contemporary Cambodian communities."

The Khmer people subsisted on rice agriculture, just as many Cambodians still do, and the water management system - designed to trap water coming down the hills in the north - was partly used for irrigation, it is believed. The village ponds, from 25 to 60ft long, were used for drinking and domestic purposes during the dry season, as well as for watering livestock.

Mr Evans said the newly discovered temples, were not grand, like those at the heart of Angkor. Most now consist only of a pile of brick rubble, plus the occasional sandstone doorframe or pedestal, which once bore a statue. But while they hold little interest for tourists, they are valuable archaeological finds - and there are nearly 100 others out there, the team believes.

Mr Evans said the temples not only had a religious function, but were centres of taxation, education and water control. "So they can tell us about the everyday life at Angkor," he said.

A succession of Khmer kings ruled the Angkor area from about 800 AD, producing the architectural masterpieces and sculpture now preserved as a World Heritage site. By the 13th century the civilisation was in decline, and most of Angkor was abandoned by the early 15th century, apart from Angkor Wat, the main temple, which remained a Buddhist shrine. When the lost city - swallowed by the jungle for centuries - was rediscovered, archaeologists were, understandably, absorbed by the need to rescue and conserve the dozen or so main temples and their bas-relief carvings. Few excavations were carried out outside the temple precinct.

"No one really thought to look beyond them and into the broader landscape, to see how people actually lived," Mr Evans said.

By the 1960s it was clear that rich archaeological pickings lay beyond the walled city. A programme was put in place to investigate the wider area, but never got off the ground because of civil war, followed by the advent of the Khmer Rouge and Pol Pot's murderous regime. It was not until the 1990s that the security situation improved, enabling work to resume. But when the international mapping team started their project, they still needed an armed escort for protection in certain areas. And even now, Mr Evans said he never steps off marked paths, because of the risk posed by unexploded landmines.

Until now, Angkor was never looked at as an extended urban area. The city was thought to consist of the central walled precinct, covering about one square mile, where tens of thousands of people lived. "No one really considered the fact that there might be an urban fabric that stretched between and beyond the temples of Angkor," Mr Evans said.

The settlement mapped by the team existed from AD500 to AD1500, and could have supported a population of up to one million people. But some of the terrain may have been sparsely populated, particularly in outlying areas. "Now we have the map, we can quantify this residential space," Mr Evans said.

"We can start to do proper demographic studies and work out how many people were living on these mounds. But we can say now, from a preliminary point of view, that it would have had a population of several hundred thousand, at least."

The city was criss-crossed by roadways and canals, and was similar to modern cities that suffer from urban sprawl. Mr Evans said: "It had the same sort of dense core and pattern of spreading out into rural areas."

The team may also have found the key to Angkor's collapse - or, at least, confirmed an existing theory: that the city "built itself out of existence". Mr Evans said: "The water management system, in particular, had the potential to create some very serious environmental problems and radically remodel the landscape. You can see the city pushing into forested areas, stripping vegetation and re-engineering the landscape into something that was completely artificial.

"The city was certainly big enough, and the agricultural exploitation was intensive enough, to have impacted on the environment. Angkor would have suffered from the same problems as contemporary low-density cities, in terms of pressure on the infrastructure, and poor management of natural resources like water. But they had limited technology to deal with these problems and failed to, ultimately, perhaps."

The team also found evidence of embankments that had been breached, and of ad hoc repairs to bridges and dams, suggesting that the water system had become unmanageable over time. Mr Evans said over-population, deforestation, topsoil erosion and degradation, with subsequent sedimenation or flooding, could have been disastrous for medieval residents.

Excavations in the next few years will examine the theory in more detail, and try to gather more data, for instance, on sedimentation in the canals.

The radar images provided by Nasa distinguished the contours of the landscape under the surface of the earth, identifying the location of roads and canals. The radar also showed up different levels of soil moisture in the rice fields. When excavations were carried out, they proved to have been the site of a canal or temple moat. The new archaeological evidence will pose a challenge for conservationists, as the current World Heritage site covers 150 square miles, which are intensively managed and protected.

Cambodian authorities, meanwhile, are grappling with the problem of how to preserve the precious ruins within the temple precinct from increasing numbers of visitors. Just 7,600 people ventured to Angkor in 1993, when it was added to Unesco's World Heritage list. Since then, with Cambodia becoming accepted as a "safe" destination, tourism has boomed. The government is expecting three million visitors in 2010, and many of those will head to the temples. Angkor Wat is now one of south-east Asia's leading attractions.

Tourism, which brought impoverished Cambodia $1.5bn (£750m) in revenue last year, is helping the country to rebuild after its long dark period. But Soeung Kong, deputy director-general of the Aspara Authority, which oversees Angkor's upkeep, told Agence France Press recently: "The harm to the temples is unavoidable when many people walk in and out of them. We are trying to keep that harm at a minimal level."

Teruo Jinnai, Unesco's senior official in Cambodia, said: "When you have such a huge mass of tourists visiting, then we are concerned about damage to the heritage site and the temples and the monuments. Many temples are very fragile."

The main problem lies in Siem Reap, the nearby town that has mushroomed in recent years to accommodate the growing numbers of tourists. There are more than 250 guesthouses and hotels, and they have been sucking up groundwater and destabilising the earth beneath Angkor. At least one monument, the Bayon temple, famous for the serene faces carved on its 54 towers, is collapsing into the sandy ground - a development confirmed by its sinking foundations, and widening cracks between its carefully carved stones.