The Khmer Empire was Southeast Asia's largest empire during the 12th century. The empire's centre of power was Angkor, where a series of capitals were constructed during the empire's zenith. 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 urban sprawl of . The city, which could have supported a population of up to one million people and Angkor Wat, the best known and best-preserved religious temple at the site, still serves as a reminder of Cambodia's past as a major regional power. The empire, though in decline, remained a significant force in the region until its fall in the 15th century.