HISTORY has been rewritten with the discovery of hidden cities that once constituted the largest empire on Earth.

The incredible find in Cambodia is being hailed as one of archaeology’s greatest achievements.

State-of-the-art airborne lasers have revealed the medieval cities that had sophisticated water systems built centuries before historians thought the technology existed.

The cities, concealed below dense tropical vegetation for hundreds of years, are extensive, with some equal in size to the modern capital of Cambodia, Phnom Penh.

The discovery has been welcomed by leading archaeologists across the world who hope it will shed light on Cambodia’s current top tourist attraction, the Angkor Wat temple ruins.

It has long been suspected that there was much more to the 12th-century temple complex and there was great excitement when an initial laser project in 2012 proved the existence of Mahendraparvata, a temple city near Angkor Wat.

The new data shows the extent of this city as well as details of a giant city complex around the temple Preah Khan of Kompong Svay.

“We have entire cities discovered beneath the forest that no one knew were there,” said Australian archaeologist Dr Damian Evans, whose paper on the findings is published today in the Journal of Archaeological Science.

Dr Evans is also due to speak today at the Royal Geographic Society in London.

WHAT DOES IT ALL MEAN?

IT is hoped the findings will explain what happened to the Khmer Empire.

“Our coverage of the post-Angkorian capitals provides some fascinating new insights on the ‘collapse’ of Angkor,” Evans said.

“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.”

Added Professor Michael Coe of Yale University: “I think that these airborne laser discoveries mark the greatest advance in the past 50 or even 100 years of our knowledge of Angkorian civilization.

“I saw Angkor for the first time in 1954, when I wondered at the magnificent temples, but there was nothing to tell us who had lived in the city, where they had lived, and how such an amazing culture was supported. To a visitor, Angkor was nothing but temples and rice paddies.”

Cambodian history expert David Chandler said Evans and his archaeological colleagues were “rewriting history”.

“It will take time for their game-changing findings to drift into guide books, tour guides, and published histories,” Chandler said.

“But their success at putting hundreds of nameless, ordinary, Khmer-speaking people back into Cambodia’s past is a giant step for anyone trying to deal with Cambodian history.”

HOW HAS THIS BEEN REVEALED?

THE data proves there were dense populations living around all the ancient Khmer temples, according to Dr Peter Sharrock of London’s School of Oriental and African Studies.

“This landscape, linked by road and canal networks, now seems to have constituted the largest empire on earth in the 12th century,” he said.

The data was gathered last year in the biggest airborne archaeological study ever made, covering 1,901 sq km.

It followed an initial lidar (light detection and ranging) project in 2012, which discovered an urban landscape that joined temple cities like Koh Ker and Beng Mealea to Angkor and provided evidence there was a city underneath Mount Kulen.

On the strength of that survey’s success Evans, of the Siem Reap’s École Française d’Extrême-Orient (EFEO), was given a European Research Council grant for the significantly larger investigation carried out last year.

In a lidar survey, laser scanners attached to a helicopter skid pad pulse the ground below cutting through obstructions like the dense jungle vegetation.

The amount of time taken by the pulse to go back to the sensor shows the elevation of each data point. This information is then downloaded and a computerised 3D model is made.

HOW IMPORTANT IS IT?

EVEN after the first survey, Evans was astonished by what he saw on his computer screen as rows of temples, evidence of settlements, irrigation canals, reservoirs, boulevards, dikes and agricultural plots appeared before him.

“To suspect that a city is there, somewhere underneath the forest, and then to see the entire structure revealed with such clarity and precision was extraordinary,” he said. “It was amazing.”

The 2012 investigation revealed a huge urban landscape at Greater Angkor and the latest one has uncovered evidence of a similar highly urbanised area at pre and post Angkorian sites.

Houses around the stone temples were made of thatch and wood and quickly rotted once the people left so the evidence of the civilisation was hidden until the laser surveys.

“The lidar quite suddenly revealed an entire cityscape there with astonishing complexity,” said Evans.

“What we had was basically a scatter of disconnected points on the map denoting temple sites. Now it’s like having a detailed street map of the entire city. We can see them with incredible precision and detail.”

Added Dr Martin Polkinghorne, of Adelaide’s Flinders University: “Cambodia after Angkor is customarily understood as a dark age. Yet, Cambodia was alive with activity after Angkor. South-east Asia was the hub of international trade between east and west.”