The ethnic name of a linguistic group inhabiting Cambodia, southern Vietnam, and parts of Thailand. Late in 6th century AD, they annexed the declining Funan Empire of south Cambodia and extended westwards. The Khmer were linguistically related to the Mon and at the height of their power ruled most of Thailand and southern Laos. The empire had its capital at Angkor in Kampuchea and it was destroyed by the Thais in about 1400 AD. Khmer was one of the most impressive civilizations of southeast Asia, known for spectacular and monumental religious architecture.