Archaeological evidence indicates that parts of the region now called Cambodia were inhabited during the first and second millennia B.C. by peoples having a Neolithic culture. By the first century A.D., the inhabitants had developed relatively stable, organized societies, which had far surpassed the primitive stage in culture and technical skills. The most advanced groups lived along the coast and in the lower Mekong River valley and delta regions, where they cultivated irrigated rice and kept domesticated animals.

Scholars believe that these people may have been Austroasiatic in origin and related to the ancestors of the groups who now inhabit insular Southeast Asia and many of the islands of the Pacific Ocean. They worked metals, including both iron and bronze, and possessed navigational skills. Mon-Khmer people, who arrived at a later date, probably intermarried with them. The Khmer who now populate Cambodia may have migrated from southeastern China to the Indochinese Peninsula before the first century A.D. They are believed to have arrived before their present Vietnamese, Thai, and Lao neighbors