Lost city

In April 2012 researchers used laser technology called Lidar to aerially scan swathes of forested land around three main areas in northwestern Cambodia: the city of Angkor in Siem Reap, the city of Koh Ker northeast of Angkor and Phnom Kulen mountain. It was the first archaeological survey of its kind in Asia.

The peer-reviewed findings of the survey, published last week in the "Proceedings of the National Academy of Sciences of the USA," revealed a dense urban sprawl around Angkor, where "the intensity of land-use and the extent of urban and agricultural space have both been dramatically underestimated" up until this point.

"The Lidar reveals clearly that the formalized, urban center of the city of Angkor extends over at least 35 square kilometers, rather than simply the nine square kilometers conventionally recognized within the walls of Angkor Thom," the paper reads.

A vast network of roads and canals

Damian Evans, an archaeologist at the University of Sydney, told DW that while researchers essentially knew the walls and moats of central temples at Angkor enclosed a grid of streets and canals, they were surprised to find that this pattern extended far beyond the temple walls.

"[The temples] were just components or nodes in … the downtown of Angkor," Evans said, adding that previously undocumented temples, roads, canals, ponds and occupation mounds were discovered in each scanned area.

Evans coordinated an eight-member consortium that conducted the survey, which included the Cambodian government's APSARA Authority, the École Française d'Extrême-Orient and the Archaeology and Development Foundation (ADF).

Messy, complicated ancient cities

The Lidar scanner transmitted millions of laser pulses that penetrated thick foliage blanketing the three areas. Researchers used software to strip away the vegetation to reveal a detailed, three-dimensional map of the landscape, including subtle impressions left by features such as roads, canals, ponds and mounds. Fieldwork was subsequently conducted to verify the Lidar data.

"This traditional view of Angkor as a nice succession of formally planned spaces, as kings laying out their city with a nice city wall or a nice temple wall and building a city inside, is fundamentally incorrect," Evans said. "Cities were much messier, much more complicated and much more intricate than people previously assumed."

David Chandler, a leading historian of Cambodia, told DW that Lidar would "enlarge our understanding of Angkor in many fascinating ways".

"Since none of the LIDARed material can be dated yet, it is hard to connect the data with the rise and fall of Angkor," he said. "Some of the new temples, however, might have valuable information."

Mountain city mapped

According to the paper, the newly discovered urban landscape on Phnom Kulen mountain corresponded with the 8th-9th century capital of Mahendraparvata, which is described in early Khmer inscriptions.

Jean-Baptiste Chevance, program director and senior archaeologist at ADF - the primary organization conducting the archaeological work at Phnom Kulen - told DW they discovered a network of roads linking previously known sites on the mountain and documented new urban features.

"Basically, we have the map of the city," he said, adding that ADF was conducting ground verification of the Lidar data. "We believe that this corresponds with the city called Mahendraparvata, because we knew the city was there before. We just didn't know which shape it had."

Evans said the Lidar data revealed that the 10th century Khmer capital of Koh Ker had an extremely sophisticated water management system.

He added that the Lidar data has implications for understanding the sustainability of the Angkor settlement, and researchers could create more accurate population growth and development models of early Khmer cities.

Heritage protection

The findings were announced as delegates gathered in the Cambodian capital Phnom Penh for the annual UNESCO World Heritage Committee meeting, in which 19 new sites were added to the World Heritage List.

Both Angkor and the 11th-century Preah Vihear temple - perched on the edge of a precipice overlooking Thailand - are included on the list for Cambodia. The heritage-protected Angkor region currently does not include Phnom Kulen, but ADF's Chevance said it was on Cambodia's tentative list for World Heritage status.

Anne Lemaistre, head of UNESCO in Cambodia, told DW the original intention was to include Phnom Kulen when Angkor was inscribed on the list 20 years ago, but security conditions at the time did not permit it.

"We didn't have access," she said. "All the roads were mined and even going to Banteay Srei [temple], which has been inscribed, was problematic." Lemaistre added that efforts to seek heritage protection for Phnom Kulen were revived last December.

Im Sokrithy, APSARA communications director and co-author of the paper, said via email that the Lidar survey's findings would add value to Cambodia's application for protected status for Phnom Kulen. He added that the findings were "an absolute revelation".

"We will use it as sources and tools for future archaeological research on the region, land-use planning, tourism planning, revising the ancient hydraulic system for controlling the water flow, avoiding the annual flooding of Angkor and the city of Siem Reap and [storing] the water for use during the dry season," Im Sokrithy said.

Further surveys hoped

Sydney University's Evans said the consortium was raising funds to conduct another Lidar survey at various sites in Cambodia in 2014.

He added that ancient cities now being uncovered in Southeast Asia and Central America bore a striking resemblance to the structure of some twentieth century cities, with densely populated downtown areas surrounded by a vast urban sprawl.

"The point is to better understand the trajectory of the growth and decline of these ancient civilizations and their cities, and the implications essentially for contemporary urban life and for urban futures," Evans said.