Amur or Amoor (Mantchu, Saghalien; Chinese, Helong Kiang), a great river of eastern Asia, which at its rise in Mongolia is known as the Argoun. Flowing N.E. the Argoun forms the boundary between Russia and China. On reaching Ust Strelka (lat. 53° 18' N., long. 121° 24' E.) it is joined by the Shilka, coming from the Trans-Baikal province of Siberia, and the united streams bear the name Amur, taking a course S.E. to the confluence of the Sangari, and thence N.E. to the Sea of Okhotsk, opposite the upper end of the I. of Saghalien. The city of Nikoliaievsk is at its mouth, and for the last 400 miles the river is wholly in Russian territory. The total length amounts to at least 2,500 miles.