The historic town of Chiang Saen, situated on the west bank of the Mekong River opposite Laos, dates from the 12th century. It was an important part of King Mangrai's Lanna Kingdom, originally being his first capital.The Golden Triangle designates the confluence of the Ruak River and the Mekong River; the junction of Thailand, Laos and Myanmar. The Mekong is the world's 10th-longest river and the 7th-longest in Asia. Its estimated length is 4,909 km (3,050 mi) and it drains an area of 795,000 km2 (307,000 sq mi), discharging 475 km3 (114 cu mi) of water annually. From the Tibetan Plateau the Mekong runs through China's Yunnan province, Burma, Laos, Thailand, Cambodia and Vietnam.