Danube (Lat. Danubius; Ger. Donau; Hung. Dana; Slav. Dunai), next to the Volga the chief river of Europe, is formed by the Brege and the Brigach, rising in the Black Forest, Baden, and uniting at Donaueschingen, 2264 feet above sea-level. It has a total length of 1740 miles, and drains 315,000 sq. m. It flows first SE., and then NE. to Ulm (1519 feet). From the junction with the Iller above Ulm it is navigable for boats of 100 tons. At Ratisbon it reaches its most northerly point, and from thence its course is generally SE. Between Ulm and Passau, where it leaves Germany, it receives the Lech, Isar, and Inn, on the right, and the Altmuhl and Regen on the left bank. At Passau its width is 231 yards, and its depth 16 feet. It flows E. to Presburg, receiving the Ens from the S., and the March or Morava from the N.; and it passes from Austria into Hungary through an opening called the Carpathian Gate. Near Waitzen it turns directly S., through the Hungarian plain, a vast sandy alluvial flat, in which it is continually forcing new channels and silting up old ones; receiving from the N. the Waag and the Gran, and the Drave from the W. Next the Danube turns again SE., and, increased by the waters of the Theiss and Temes from the N., sweeps past Belgrade, where it is joined by the Save, and forms the boundary between Hungary and Servia. Before touching the Roumanian frontier its width is greatly contracted and interrupted by eight rapids with rocky shoals. The most difficult passage is the shortest (l 1/2 mile) of the eight - the ' Iron Gate,' properly so called, below Orsova. In 1890-95 the Hungarian government undertook, at a cost of £800,000, to improve, by blasting rocks and widening the course, the navigation here. In Wallachia the Danube flows in a wide stream, constantly broadening into a lake, or overspreading its banks with swamps. It forms the northern boundary of Bulgaria as far as Silistria; and from here it turns northward, skirting the Dobruja, and flows between marshy banks to Galatz, receiving on the way the Jalomitza and the Sereth. From Galatz it flows E., and, after being joined by the Pruth from the N., SE. to the Black Sea. The delta is a vast wilderness (1000 sq. m.) cut up by channels and lagoons; the farthest mouths are 60 miles apart. Two-thirds of the Danube's volume passes through the Kilia, which, like the southern or St George branch, forms a double channel near the outlet; and so ships enter by the middle or Sulina mouth, deepened to 20 feet and straightened in 1858-1903. The steel cantilever bridge across the river (2878 metres) at Tchernavoda is one of the great railway bridges of the world. To defend Vienna against risk of inundation, the course of the Danube skirting it was, in 1868-81, diverted into an artificial channel. Similar works have been undertaken near Pesth. The Danube has about 400 tributaries, 100 of them navigable by the fleet of the Danube Steam Navigation Company (1830). The Danube is connected with the Rhine by means of the Ludwigs-Canal (1844), and with the Elbe by means of the Moldau and Muhl, and canals. See F. D. Millet, The Danube from the Black Forest to the Black Sea (1892).