The sparse evidence for a Pleistocene human occupation of present day Cambodia are quartz and quartzite pebble tools found in terraces along Mekong River, in Stung Treng and Kratié provinces, and in Kampot Province, but their dating is not reliable.
Some slight archaeological evidence shows communities of hunter-gatherers inhabited Cambodia during Holocene: the most ancient Cambodian archeological site is considered to be the cave of Laang Spean, in Battambang Province, which belongs to the so-called Hoabinhian period. Excavations in its lower layers produced a series of radiocarbon dates as of 6000 BC.
Upper layers in the same site gave evidence of transition to Neolithic, containing the earliest dated earthenware ceramics in CambodiaArcheological records for the period between Holocene and Iron Age remain equally limited. Other prehistoric sites of somewhat uncertain date are Samrong Sen (not far from ancient capital of Oudong), where first investigations started just in 1877, and Phum Snay, in the northern province of Banteay Meanchey.Prehistoric artifacts are often found during mining activities in Ratanakiri.
The most outstanding prehistoric evidence in Cambodia however are probably "circular earthworks", discovered in the red soils near Memot and in adjacent region of Vietnam as of the end of the 1950's. Their function and age are still debated, but some of them possibly date from 2nd millennium BC at least.
A pivotal event in Cambodian prehistory was the slow penetration of the first rice farmers from North, which begun in the late 3rd millennium BC. They probably spoke ancestral Mon-Khmer.
Iron was worked by about 500 BC. The most part of evidence come from Khorat Plateau, Thai country nowadays. In Cambodia some Iron Age settlement were found beneath Angkorian temples, like Baksei Chamkrong, others were circular earthworks, like Lovea, a few kilometers north-west of Angkor. Burials, much richer, testify improvement of food availability and trade (even on long distances: in the 4th century BC trade relations with India were already opened) and the existence of a social structure and labor organization.