The City Built on Water
At its peak in the 13th century, the metropolitan area of Angkor was the largest pre-industrial city in the world. It sprawled across nearly 1,000 square kilometers and housed an estimated 750,000 to 900,000 people. This megacity was made possible by one of history's most sophisticated water management systems. Khmer engineers constructed a massive network of canals, embankments, and huge reservoirs called barays to control the seasonal monsoon rains. The West Baray, for instance, is an artificial lake measuring 8 by 2.1 kilometers that is still visible today.
This complex "hydraulic city" was designed to collect and store water during the wet season for use in the dry season, allowing for multiple rice harvests per year to feed its large population. The water system was for agriculture; it was also a defense mechanism, a transportation network, and a representation of the Hindu cosmos, with temples like Angkor Wat represent Mount Meru surrounded by a cosmic ocean—its 190-meter-wide moat. For centuries, this mastery of water was the foundation of the Khmer Empire's power.
A System Under Stress
The end of Angkor was not a single event, but a long process that began in the 14th century. The conventional narrative points to the year 1431, when armies from the Siamese kingdom of Ayutthaya sacked the capital. This invasion was the culmination of decades of growing external pressure and military defeats that weakened the empire. Following the 1431 attack, the Khmer court relocated south towards modern-day Phnom Penh, a move that was a political shift away from Angkor.
Archaeological evidence points to a different story involving severe environmental stress. Tree-ring data reveals that Southeast Asia experienced extreme climate shifts starting in the mid-1300s. A prolonged and severe drought lasting decades was punctuated by years of intense monsoon rains. This climatic volatility would have been catastrophic for Angkor's rigid water management system. The drought would have depleted water stores necessary for agriculture and daily life, while the subsequent deluges would have overwhelmed the infrastructure, causing canals to clog with sediment and dams to break. This cascade of failures in the water network, which the city depended upon for its survival, likely led to crop failures and destabilized the very foundation of the king's authority. The abandonment of Angkor was not an abrupt collapse but a gradual transformation, driven by both a failing infrastructure and external military pressures.