The Tuul River or Tula River (, ; in older sources also Tola) is a river in central and northern Mongolia. Sacred to the Mongols, the Tuul is generally called the Khatan (Queen) Tuul in Mongolian. It is 704 km long and drains an area 49,840 square km. The river is called the "Duluo river" in the Book of Sui, a Chinese historical work completed in 636 AD. The Secret History of the Mongols (1240 AD) frequently mentions a "Black Forest of the Tuul River" where the palace of Wang Khan was located. The Ming dynasty (1368–1644) was established by the progressive expulsion of the Mongol Empire from China. After capturing Beijing, the Ming's founding Hongwu Emperor defeated the Mongols at the Tula River in 1372, driving them back to the Orhon River. The following Hongwu Emperor would find it necessary to defeat the Oirats at the river Tula again in 1414.