Mastery over Water. One of the major success of the Angkor Empire was due to its mastery over the control of water from the Mekong River. Being situated in the tropical Monsoon zone, the Angkor was subjected to a wet season with heavy rainfall during Monsoon and a dry season during the off-Monsoon period.
Due to their engineering genius, the ancient Khmer built extensive irrigation and drainage system in order to manage the excessive water from the flood. This water was stored in the huge reservoirs such as the East and West Baray, and irrigated to the farmlands during the dry period. In this way, the Angkor were able to cultivate and harvest rice crops two or three times in one year. Such a high productivity of rice crops in a year helped to strengthen the country's economy significantly, and thus enhanced its prosperity. This enabled the god-king of the Angkor Empire to mobilize large number of laborers and slaves to undergo temples construction, several of which required over ten thousands of laborers and took them from two to three decades to complete.
In addition, the Angkor kings were able to recruit manpower to serve in military which play a major role, not only in defending the throne, but in invading the neighbors. The Angkor kingdom expanded its territory vigorously and became a strong regional empire.
The two major reservoirs at the Angkor are the East and West Baray. The East Baray has long been dry whereas the West Baray is still in use today. Two more reservoirs had been discovered recently by the aerial photographs.
It was estimated by George Grosliers, a French archaeologist, that the total agricultural land of the Angkor Empire was about 70,000 hectares. Being used to cultivate crop two or three times in one year, the land was able to support the densely populated Angkor kingdom. This mastery over the water is one of the major factor for the rise of Khmer Civilization.