Northeast Thailand (Isan) was incorporated into the polity of Angkor around the end of the first millennium a.d. Well before this time, local communities in the Phimai region had adopted important activities such as the use of inscriptions and the construction of religious architecture in permanent materials. In 1998, the Origins of Angkor Project undertook an archaeological excavation at the most important Khmer temple in Thailand, the Prasat Hin Phimai. The excavation recovered late prehistoric ceramics and remains of an early brick structure, probably religious in nature, which had been re-used as part of the foundation of the sandstone Angkorian temple.