The most defining natural attractions in Kanchanaburi is arguably the Three Pagodas Pass, a break in the Thanon Thongchai Mountain Range that divides Thailand and Myanmar. Buddhism is thought to have first arrived in Thailand from India through the pass the A.D. 3rd century. In the 13th century the pass was controlled by the Khmer of Angkor, who built a fort there ( a Khmer temple from the time has been restored as a tourist attraction). The kingdom of Ayutthaya also built a military garrison in the area, yet it was through the pass that the Burmese swept into Siam and razed Ayutthaya in the 18th century. In World War II, the Japanese built a railway through the pass using forced labor, including western POWs. Later known as the Death Railway, the line included an infamous bridge crossing the Kwai River.