("Dīsos"), a great river of Central Asia, called by the natives on its banks the Amoo, and by Turkish and Persian writers the Jihon, rises in a lake called Sari-Kol, about 15,600 ft. above the sea, among the Pamir Mountains or Tartaric Caucasus, in Badakhshan; Lat. 37° 48' N., Long. 73° 40' E. The river issues from the west end of the lake, and thence flows N.W. until it falls into the Sea of Aral. Near its origin the Oxus receives several tributaries from the Hindoo Koosh; and during its course there are many large affluents of which comparatively little is known. Its whole length is about 1300 miles, and it drains an area estimated at about 221,256 square miles. The most remarkable fact connected with this river is, that the testimony of antiquity is almost unanimous in representing the Oxus as flowing into the Caspian. Pomponius Mela is the only ancient writer whose description of the Oxus agrees with its modern course; but his single testimony cannot be considered of much value, since both Strabo, who lived but a short time before him, and Ptolemy, within a century after, assert that in their time it followed a different course; while the former writer informs us that merchandise was conveyed from the East by this river to the Caspian, and thence to the Euxine. It is therefore the opinion of most modern authorities, that the river did formerly discharge itself into the Caspian; and some traces of its mouths, it is thought, have been discovered in the Bay of Balkan. Humboldt supposes, that down to the time of Alexander the Sea of Aral and the Caspian formed one great sea; that by some violent convulsion, or by the gradual effects of evaporation, they were separated; and that the Oxus then had two branches, one flowing to the Caspian, and the other to the Aral, the former of which has become dried up, so that the latter only now remains.