The Kunlun Mountains constitute one of the longest mountain chains in Asia, extending for more than 3,000 kilometres (1,900 mi). In the broadest sense, the chain forms the northern edge of the Tibetan Plateau south of the Tarim Basin. Located in Western China, the Kunlun Mountains have been known as the "Forefather of Mountains" in China. The exact definition of the Kunlun Mountains varies over time. Older sources used Kunlun to mean the mountain belt that runs across the center of China, that is, Altyn Tagh along with the Qilian and Qin Mountains. Recent sources have the Kunlun range forming most of the south side of the Tarim Basin and then continuing east, south of the Altyn Tagh. Sima Qian (Records of the Grand Historian, scroll 123) says that Emperor Wu of Han sent men to find the source of the Yellow River and gave the name Kunlun to the mountains at its source. The name seems to have originated as a semi-mythical location in the classical Chinese text Classic of Mountains and Seas.