The Khmer Empire, now known as Cambodia, was perhaps the most powerful empire in Southeast Asia. The empire, which grew out of the former kingdom of Chenla, at times ruled over and/or vassalized parts of modern-day Laos, Thailand, and southern Vietnam. During the formation of the empire, the Khmer had close cultural, political and trade relations with Java, and later with the Srivijaya empire that lay beyond Khmer's southern border. Its greatest legacy is Angkor, in present-day Cambodia, which was the site of the capital city during the empire's zenith. Angkor bears testimony to the Khmer empire's immense power and wealth, as well as the variety of belief systems that it patronised over time. The empire's official religions included Hinduism and Mahayana Buddhism, until Theravada Buddhism prevailed, even among the lower classes, after its introduction from Sri Lanka in the 13th century. Recently satellite imaging has revealed Angkor to be the largest pre-industrial urban center in the world.
The history of Angkor as the central area of settlement of the historical kingdom of Kambujadesa is also the history of the Khmer from the 9th to the 13th centuries.
From Kambuja itself — and so also from the Angkor region — no written records have survived other than stone inscriptions. Therefore the current knowledge of the historical Khmer civilization is derived primarily from:
Angkor (Khmer: អង្គរ, "Holy City") is a region of Cambodia that served as the seat of the Khmer Empire, which flourished from approximately the 9th to 15th centuries. The word Angkor is derived from the Sanskrit nagara (नगर), meaning "city". The Angkorian period began in AD 802, when the Khmer Hindu monarch Jayavarman II declared himself a "universal monarch" and "god-king", until 1351, when Angkor first fell under Ayutthayan suzerainty, to 1431, when Ayutthaya put down a rebellion and sacked the Khmer capital, causing its population to migrate south to Longvek.
The ruins of Angkor are located amid forests and farmland to the north of the Great Lake (Tonlé Sap) and south of the Kulen Hills, near modern-day Siem Reap city (13°24′N, 103°51′E), in Siem Reap Province. The temples of the Angkor area number over one thousand, ranging in scale from nondescript piles of brick rubble scattered through rice fields to the magnificent Angkor Wat, said to be the world's largest single religious monument. Many of the temples at Angkor have been restored, and together, they comprise the most significant site of Khmer architecture. Visitor numbers approach two million annually, and the entire expanse, including Angkor Wat and Angkor Thom is collectively protected as a UNESCO World Heritage Site.