DANUBE (ancient, DANUBIUS ; German, DONAU ; Hungarian, DUNA), the second river of Europe, originating in two small streams, the Brege and the Brigach, rising on the east slope of the Schwarzwald, a mountainous region of southwest Germany (the Black Forest), in the Grand-duchy of Baden, at an elevation of 2,850 feet above sea-level, and uniting at Donau eschingen. Its general course is from west to east, and it flows into the Black Sea by four dif ferent outlets, called respectively the Kilia, Stambool, Sulina and the Edrillis or Saint George's mouths. The Sulina mouth or channel is the deepest. The extent of the basin of the Danube is about 300,000 square miles, and its total length is about 1,875 miles. The Danube basin comprises portions of Austria-Hungary, Germany, Serbia, Bosnia, Rumania and Bul garia. From its source it flows northeast to Ratisbon, in Bavaria, whence it takes a south east course, by Vienna and Pressburg, to Wait zen, in Hungary. Here the course is changed to nearly due south of the point where it re ceives the waters of the Drave, near Esseg, in Slavonia; thence it flows southeast' to Belgrade, on the north boundary of Serbia, and for some distance it forms the boundary between Serbia and Austria. The course continues in an east erly direction to Orsova (the Iron Gate), where it changes to southeast, then again nearly east, forming for a long distance the boundary line between Rumania and Bulgaria. At Silis tria, in Bulgaria, it turns more to the north, through Rumania to Galatz, then :southeast be tween Rumania and Bessarabia, in Russia, and finally into the Black Sea.
The great basin of the Danube has been divided into four minor basins. The first con sists of a vast plateau 1,640 feet above sea-level, 150 miles in length and 125 miles broad, sur rounded by mountains, and comprising a por tion of the principality of Hohenzollern, part of the kingdom of Wurtemberg and the greater part of the kingdom of Bavaria. This tract is by far the most fertile and most populous through which the Danube passes on its course. The principal branches within this space are the Iser and Lech. A canal connecting the Altmillil with the Regnart, an affluent of the Main, gives access to the Rhine.
The second basin belongs to the empire of Austria, having Vienna nearly in its centre, and comprising the archduchy of Austria, Hungary as far east as Waitzen, and Styria. It is very irregular and is bounded by very high moun tains. The soil is rich in mineral products and the climate one of the best in Europe. The prin cipal branches in this basin are the March or Morava and the Enns — the former from the left and the latter from the right. The Danube here passes through a succession of the most picturesque scenery.
The third basin of the Danube comprises Hungary east of Waitzen and the crownland of Transylvania, and consists of an immense plain, almost without undulations of any kind, and only 394 feet above the sea-level. It is inter sected by large rivers with marshy banks, and interspersed with stagnant pools, saline and sandy wastes. It comprises about one-half of
the entire basin of the Danube. The marshes cover a space 3,053 square miles. The princi pal branches in this basin are the Save, the Drave and the Morava. From Budapest to Bel grade the river passes through an immense plain covered with sand and alluvium, through which it is constantly forming new channels and filling up the former ones. Below Moldava it passes for 60 miles through a succession of rapids and shallows interspersed with rocks and sandbanks, where it has cut a passage for itself through the cross chain of hills which connect the Carpathian Mountains with the Alps; and between Drenkova in Hungary and Scala Kla dova in Serbia, the navigation is partially inter rupted by three great rapids, the principal or last and lowest of which is the famous Iron Gate, where the stream rushes through a narrow chan nel between stupendous •rocks, ending with a series of whirlpools, eddies and smaller falls. By the removal of various obstructions vessels drawing nine feet have long been able to pass at certain seasons; and by works carried out in 1890-96, and extending over some 50 miles, a permanent waterway has been secured.
The fourth basin comprises Rumania, a por tion of Bessarabia and Bulgaria. This tract is flat, inundated and marshy along the banks of the river; dry and mountainous on the borders of the basin. The principal branches in this basin are the Aluta, Sereth and Pruth. In the lower part of its course the Danube increases in width from 1,400 to 2,100 yards; and in one part it forms an expanse of water like a sea and is studded with islands. Excepting between Drenkova and Kladova, the Danube may be said to be navigable for steamers from Ulm to the sea, although in some places navigation is ren dered difficult by shallows and sandbanks, in tersected by narrow and intricate channels. The outlets of the Danube are separated from each other by several low islands covered with reeds and trees. The greater part of the ships bound up the river enter it by the Sulina mouth. The Danube has 60 navigable tributaries, and its volume of water is nearly equal to that of all the rivers that empty themselves into the Black Sea taken together. Its rapidity is in many places above Orsova so great as to render navi gation difficult, but below that point its current is less rapid. A number of steamers now ply on the river between its principal towns. The prin cipal towns on the banks of the Danube are Urn, in Wiirtemberg; Regensburg (Ratisbon) and Passau, in Bavaria; Linz and Vienna, in Austria; Pressburg, Budapest and Peterward ein, in Hungary; Belgrade, in Serbia; Widin, Nicopolis, Rustchuck and Silistria, in Bulgaria; Brahilow and Galatz, in Rumania.
Under the terms of the Peace of Paris in 1856, the Danube was declared free to the ships of all nations; and at the Berlin Congress of 1878 it was agreed that no ships of war should navigate below the Iron Gate.