The Khmer Empire, which is located in modern day Cambodia was a main power Southeast Asian mainland for centuries. By the 800s, Khmer had conquered neighboring kingdoms and made their own empire. This empire reached its peak of power around 1200. Improvement of rice cultivation and elaborate irrigation ways helped the Khmer become more prosperous. These advances made it possible to grow three or four crops of rice a year instead of just one. Their capital, Angkor was where rulers built extensive city-and-temple complexes. Angkor Wat was one of those complexes. and it is one of the world's greatest architerctural achievements. It was built as a dedication to the Hindu god Vishnu, and used as an observatory.