Watch on 123Movies. Uncover the lost secrets of a once-mighty empire. The city of Angkor, the seat of the great Khmer Empire in Southeast Asia for 500 years, was once the biggest city in the world. For centuries, this incredible civilization flourished, building the largest religious monument on Earth, Angkor Wat, and mastering urban engineering in a challenging landscape. But then it was mysteriously abandoned, swallowed by the jungle. Now, cutting-edge technology and new discoveries are finally revealing how this astounding empire rose to global prominence – and what likely led to its devastating collapse.