Angkor was the capital of the Khmer Empire, which flourished from approximately the 9th to 13th centuries. The word Angkor is derived from the Sanskrit nagara meaning 'city'. The Angkorian period began in AD 802, when the Khmer Hindu monarch Jayavarman II declared himself a 'universal monarch' and lasted until 1431, when Ayutthayan invaders sacked the Khmer capital, causing its population to migrate south to the area of Phnom Penh.