The great south-eastward-flowing river of Europe, 1750 m. in length, rises in the Black Forest, and is divided into Upper, Middle, and Lower; the Upper extends as far as Pressburg, begins to be navigable to Ulm, flows NE. as far as Ratisbon, and then bends SE. past Vienna; the Middle extends from Pressburg to the Iron Gate, enclosing between its gorges a series of rapids, below Orsova; and the Lower extends from the Iron Gate to the Black Sea. It receives numerous tributary rivers, 60 of them navigable, in its course; forms with them the great water highway of the SE. of Europe, and is of avail for traffic to all the races and nations whose territories it traverses; the navigation of the river is free indeed to all nations.