The temples of the Angkor area number over one thousand, ranging in scale from piles of rubble scattered through the jungle to the world’s largest single religious monument, Angkor Wat. It was originally constructed as a Hindu temple dedicated to the god Vishnu for the Khmer Empire, gradually transforming into a Buddhist temple towards the end of the 12th century. In 2007, an international team of researchers using satellite photographs and other modern techniques concluded that Angkor had been the largest pre-industrial city in the world, with an elaborate infrastructure system connecting an urban sprawl of at least 1,000 square kilometres.