The Megalithic Culture is mostly limited to western Island Southeast Asia, with the greatest concentration being western Indonesia. While most sites aren't dated, the age ranges of dating sites are between the 2nd to 16th century CE. They are divided into two phases. The first is an older megalithic tradition associated with the Neolithic Austronesian rectangular axe culture (2,500 to 1,500 BCE); while the second is the 3rd or 4th century BCE megalithic tradition associated with the (non-Austronesian) Dong Son culture of Vietnam. Prasetyo (2006) suggests that the megalithic traditions are not originally Austronesian, but rather innovations acquired through trade with India and China, but this has little to no evidence in the intervening regions in Thailand, Vietnam, and the Philippines.