A lost medieval city that thrived on a mist-shrouded Cambodian mountain 1,200 years ago has been discovered by archaeologists using revolutionary airborne laser technology.
In what it called a world exclusive, The Sydney Morning Herald said the city, Mahendraparvata, included temples hidden by jungle for centuries, many of which have not been looted.
A journalist and photographer from the newspaper accompanied the "Indiana Jones-style" expedition, led by a French-born archaeologist, through landmine-strewn jungle in Phnom Kulen, in the Siem Reap region that is home to Angkor Wat, the largest Hindu temple complex in the world.
The expedition used an instrument called Lidar - light detection and ranging data - which was strapped to a helicopter that criss-crossed a mountain north of Angkor Wat for seven days.
The device provided data that matched years of ground research by archaeologists.
It effectively peeled away the jungle canopy using billions of laser pulses. Researchers got to see structures that were in perfect squares, completing a map of the city that years of painstaking ground research had been unable to achieve.
The work helped reveal the city that reportedly founded the Khmer Empire in AD802.
It uncovered more than two dozen previously unrecorded temples and proof of ancient canals, dykes and roads using satellite navigation co-ordinates gathered from the instrument's data.
Jean-Baptiste Chevance, director of the Archaeology and Development Foundation in London who led the expedition, told the newspaper it was known from ancient scriptures that a great warrior, Jayavarman II, had a mountain capital, "but we didn't know how all the dots fitted, exactly how it all came together".
The discovery is set to be published in the Proceedings of the National Academy of Sciences in the United States.
Damian Evans, director of the University of Sydney's archaeological research centre in Cambodia, which played a key part in developing the Lidar technology, said there might be important implications for today's society.
"One theory we are looking at is that the severe environmental impact of deforestation and the dependence on water management led to the demise of the civilisation," he said. "Perhaps it became too successful to the point of becoming unmanageable."
The Herald said the trek to the ruins involved traversing rutted goat tracks and knee-deep bogs after travelling high into the mountains on motorbikes.
Everyone involved was sworn to secrecy until the findings were peer-reviewed.
Evans said it was not known how large Mahendraparvata was because the search had so far covered only a limited area.
More funds were needed to broaden it out, he said. "Maybe what we see was not the central part of the city, so there is a lot of work to be done to discover the extent of this civilisation."
Chuch Phoeun, secretary of state at Cambodia's Ministry of Culture, said: "We need to preserve the area because it's the origin of our culture."
Angkor Wat was at one time the world's largest pre-industrial city, and is considered one of the ancient wonders of the world.
It was built from the early to mid-1100s by King Suryavarman II at the height of the Khmer Empire's power.