Here in the Cambodian jungle, lies a kingdom from a fairy tale. At its center sprawled a metropolis of incredible size, power, beauty, and wealth-that, to the outside world, simply vanished.
For 150 years, scientists have crisscrossed the lower reaches of the Mekong River pursuing answers to one of archeology's most compelling mysteries. Who were the people that built this far-reaching empire? And why - why did they abandon their grand city-state?
In 1860, following the trail of Buddhist pilgrims, French naturalist Henri Mouhot (Moo-oh ) arrived at the vast ruins of this ancient metropolis. He found a ghost-like city of abandoned avenues and colossal buildings-as grand as anything left by Greece or Rome.
And no temple is bigger than Angkor Wat, still to this day the largest religious monument in the world. Built by King Suryavarman the Second in the 12th century as his tomb. Sprawling across 500 acres, it's four times larger than the Vatican, twice as high as the Tower of London with more stone than the Great Pyramid of Giza. While it took Europeans 200 years to build their great cathedrals, an ingenious network of canals allowed the Khmer people to complete Angkor Wat in less than 35.
The causes of Angkor's collapse may be ancient. But in today's world of sprawling mega-cities, knowing why Angkor failed is more crucial than ever. After 150 years of painstaking fieldwork, archeologists discovered something important. The construction of Angkor was constant, each king building on the success of the one before.
The reasons for its rise and decline can provide lessons in sustainability for many modern mega-cities, facing today's climate shifts with crumbling infrastructures and degraded sources of water.
A place of fascination and wonder, Angkor remains a breathtaking monument to human ingenuity. But it stands also as a stark reminder of the relentless future ingenuity a sustainable world will demand.