Angkor

The Angkor region of Cambodia served as the center of power for the Khmer Empire from 800 AD well into the 1400s. The region was abandoned after a slow decline that ended with an invasion by a Thai army in 1431, leaving the massive city and its thousands of Buddhist temples to be reclaimed by the jungle. The city lay relatively untouched until the 1800s, when a group of French archeologists began to study and restore it. Angkor and its surroundings– which rival Los Angeles in size– have since been recognized as the biggest pre-industrial city in the world, and its famed temple of Angkor Wat is commonly considered to be the largest religious monument in existence.