It wasn't until the first century AD that the indigenous population began to adopt advanced concepts of rice cultivation, religious beliefs and social structure and to establish themselves as a civilization worthy of note. This transformation owes much to the visiting Indian traders, en route to China, who brought ideas as well as goods to the region. Thus, the area to the west of the Mekong Delta began establishing itself as an important commercial settlement centred around the port of Oc Eo (now in Vietnam). The civilization became known by the Chinese as Funan.

The Indianized Funan port community enjoyed prosperity for several centuries, but gradually declined in importance from the sixth century, as farmers began to move away and cultivate the fertile areas around the Mekong and Tonle Sap. From this time, the Chinese referred to the inhabitants as the Chenla . Although this term implies a cohesive culture, the Chenla actually consisted of small, disparate fiefdoms operating independently. It took the foresight and inspirational guidance of Jayavarman II, recently returned from Indonesia, to guide these rival factions towards a prosperous unification.