DANUBE (German, Bonaw ; Hungarian, Buna ; Latin, Banubius, or Banuvius, and in the lower part of its course, Ister), the largest river of Europe next to the Volga, traversing the southern part of Germany, Austria, Hun-gary, and the northern part of Turkey, and falling into the Black Sea after a course of about 1750 (or, including its windings, 2000) miles. Its basin, which comprises a territory of nearly 300,000 square miles, is bounded by the Black Forest, some of the minor Alpine ranges, the Bohe-mian Forest, and the Carpathian mountains on the north, and by the Alps and the range of the Balkan on the south. The Danube is generally considered to be formed by the union, at Donaueschingen, of the Brigach and the Brege, two mountain streams from the Black Forest; though a third stream, originating in a spring in the palace garden of Donaueschingen, at a height of about 2850 feet above the sea, is by some held to be the true source. It seems probable, according to the investigations of Professor Knop of Carlsruhe, that at Immardingen the infant river loses a good part of its waters in the fissures of the soil, and thus gives rise to the Aach, which flows south and joins the Bhine. After passing N.E. through the kingdom of Wiirtemberg and part of Bavaria to Ratisbon, it turns to the S.E., and maintains that direction till it approaches Lintz in Austria. From this town its course is in the main easterly to Hungary, which it enters a little above Presburg. From Presburg it flows S.E. through the lesser Hungarian plain to its confluence with the Raab, whence it runs E. to Waitzen. At Waitzen it turns S., and flows with a slow current and numerous windings through the greater plain of Hungary for nearly 2|r degrees of latitude. After its junction with theDrave it again takes a general S.E. direction to Orsova, where it leaves the Austrian territories by the famous pass of the Iron Gate, with once formidable rapids. From Orsova, its course is generally S. by E. to Kalafat, thence mostly E. by S. to Sistova; it there takes an E, by N. direction to Bassova, then turns N. to Galatz, and finally eastward to the Black Sea. Among its 400 tributaries, of which upwards of 100 are navigable, the principal are—on the right, the Iller, Lech, Iser, Inn, Ens, Raab, Drave, Save, Morava, Timok, Isker, Vid, and Jantra ; and on the left, the Altmiihl, Nab, Regen, March, Waag, Gran, Theiss, Temes, Chyl, Aluta, Jalomnitza, Sereth, and Pruth. The Danube communicates with the Rhine by means of the Ludwigs-Canal, which unites the Altmiihl with the Main, with the Elbe by means of the Moldau and other canals, and with the Theiss, its own tri-butary, by means of the Franzens-Canal. The upper course of the river is regularly frozen over all winter ; and even the lower reaches are usually closed for a considerable period. According to a British consular report in 1873, the river at Galatz during the thirty-seven years from 1837 to 1873 remained open all winter only eight times, namely, in 1839, 1846, 1852, 1853, 1854, 1860, 1867, and 1873;
the date of the complete freezing over varied from Dec. 7 to Feb. 14; and the breaking up of the ice occurred as early as Jan. 18, and as late as March 21. This last event always causes great anxiety to the inhabitants ; for, if the thaw begins in the upper part of the stream, the waters rush down with tremendous fury, and frequently do incalculable damage. When such a catastrophe is appre-hended, watchmen are stationed on eminences along the banks of the river, to give notice by alarm guns when the ice is broken.

At Ulm the Danube receives the Iller, and thus, at a height of 1400 feet above the sea, becomes navigable for flat-bottomed boats of 100 tons. From Donauwörth to Passau it traverses the Bavarian plain, leaving which it intersects a mountainous region till it reaches Vienna. At Passau it is 800 feet above the level of the sea, and at Vienna 450. From Vienna to the mouth of the Drave it flows through an expanse of plain country, broken only in a few places, as at Presburg, Buda, and Waitzen. At Isakcha the channel is 1700 feet broad and 50 feet deep. At extreme low water the total current is 70,000 cubic feet per second, at ordinary low water 125,000, at ordi-nary high water 324,000, and during extraordinary flood 1,000,000, and thus, on a general average from the obser-vations of 10 years, 207,000 feet per second. The total amount of alluvium annually carried down by the river is calculated at 67,760,000 cubic feet; and, according to M. Desjardins, the advance of the coast thus produced during the Christian era is about 9 or 10 miles. About 15 miles below Isakcha the river breaks up into two branches, of which the northern or Kilia branch forms an irregular network of channels on its way to the sea, and, after re-uniting into one, gives rise to a secondary delta with nine or ten arms; while the southern or Tultcha branch subdivides before long into the central or Sulina branch and the southmost or St George's. The delta thus formed com-prises an area of about 1000 square miles, almost totally destitute of cultivation, and broken in all directions by swamps and fresh-water lakes. Of the total burden of the river it was calculated in 1857 that the Kilia branch carried down seventeen twenty-sevenths, the Sulina branch two twenty-sevenths, and the St George's eight twenty-sevenths ; but since that date the Tultcha St George's branch has grown shallower, and the volume of the Kilia has increased to about eighteen twenty-sevenths, or two-thirds of the whole discharge.

In the course of the present century a good deal has been done to render the Danube more available as a means of communication. In 1816 Austria and Bavaria made arrangements for the common utilization of the river; and since then both Governments have been liberal in their outlays for its improvement. In 1830 steam-boats wrere introduced between Vienna and Pesth, under the encouragement of Count Szechenyi, a steam-boat company having been started in 1828 by two Englishmen, Andrews and Prichard. In 1834 the boats descended as far as Orsova, and in 1835 they began to reach Galatz. About the same time the draining of the Donaumoos, between Neuburg and Ingolstadt, which had been commenced in 1791, was successfully prosecuted. In 1844 the Ludwigs-Canal was completed at a cost of 400,860,000 dollars ; and in 1845 and 1853 the removal of the rocks which still, in spite of the labours of Joseph IL, obstructed the river below Greia was finally achieved. In 1866 an imperial commission was established for the rectification of the river bed in the neighbourhood of Vienna; and the proposal to construct a new channel, supported by the engineers Abernethy and Sexauer, was ultimately chosen as the most promising scheme. In terms of the Peace of Paris, March 1856, the river not only was placed under the protection of international law, and declared free to the ships of all nations, but a commission was constituted in November of that year for the purpose of putting the deltaic portion in the best possible state for navigation. It took the title of "European Commission of the Danube," and consisted of the following representatives of the seven powers who had signed the treaty :—the Chevalier de Becke for Austria, Major Stokes,, R.E., for England, Monsieur Engelhardt for France, Herr Bitter for Prussia, Baron d'Offenburg for Bussia, the Marquis d'Aste for Sar-dinia, and Omar Fetzi Pasha for Turkey. Sir Charles Hartley was appointed engineer-in-chief. The commission fixed its seat at Galatz, and began its labours by estab-lishing an engineering factory and depot at Tultcha, and constructing a telegraph line between Sulina, Tultcha, and Galatz ; but, after a discussion which lasted from Decem-ber 1857 to April 1858, the delegates could not come to an agreement in regard to the relative claims of the St George's and the Sulina mouths, and had to refer the question to their respective Governments. A technical commission appointed by France, England, Prussia, and Sardinia decided unanimously in favour of St George's, but recommended, instead of the embankment of the natural channel, the formation of an artificial canal closed by sluices at its junction with the river, and reaching the sea at some distance from the natural em-bouchure. The choice of St George's made by this com-mission was adopted at Galatz in December 1858, and six of the seven representatives voted for the canalization; but, owing to various political and commercial considera-tions, it was ultimately decided to do nothing more in the meantime than render permanent and effective the pro-visional works already commenced at the Sulina mouth. These consisted of two piers, forming a seaward prolongation of the fluvial channel, and had been commenced in 1858, according to Sir Charles Hartley's plan calculated for a period of six or eight years. In their permanent form they were completed on 31st July 1861, having required for their construction 200,000 tons of stone, and 12,500 piles. The northern pier had a length of 4631 feet, the southern of 3000, and the depth of water in which they were built varied from 6 feet to 20 feet. At the commence-ment of the works the depth of the channel was only 9 feet, but by their completion it had increased to 19 feet. Ten years afterwards it was found expedient to make the total length of the piers 5332 and 3457 feet. Various minor rectifications of the channel were also effected, and in 1865 a lighthouse was established in 44° 51' N. lat. and 29° 36' 32" E. long. The expenses of 1857, 1858, 1859, and part of 1860 were provided by the Ottoman Empire; but since that year the commission has been mainly indebted to a tax on the shipping of the river. Of what value the works of Sulina have proved may be shown by the fact that of 2928 vessels navigating the lower Danube in 1855, 36 were shipwrecked, while of 2676 in 1865 only 7 were thus unfortunate. By the treaty of March 13, 1871, signed at London by the seven powers, the commission is to exist for twelve years, and the works accomplished under its superintendence are declared permanently neutral. It is independent of the Boumanian Government, and has various sovereign powers over the Danube below Isakcha, such as the control of the police, the collection of taxes, and the disposal of its revenue. The same treaty autho-rizes the permanent commission of the riparian states (Austria, Bavaria, Wiirtemberg, Turkey, Moldavia, Walla-chia, and Servia), which commenced its labours at Vienna in 1856, to collect a tax from all the vessels navigating the river, in order to pay the expenses of the proposed removal of the obstructions that still render dangerous the passage of the Iron Gate.

Literature. —Marsiglius, Danubius Pannonico-Mysicus, Tlie Hague, 1726 : Schulte's Donaufahrten, 1819-29 ; Planche, Descent of the Danube, 1828 ; Szechenyi, lieber die Donauschifffahrt, 1836 ; A. Müller, Die Donau vom Ursprünge bis zu den Mundungen, 1839-41 ; J. G. Kohl, Austria, the Danube, éc, London, 1844, and Die Donau,
Trieste, 1853-4 ; G. B. Eennie, Suggestions for the Improvement of the Danube, 1856 ; Sprat, Report on the Delta of the Danube, 1857 ; Sir C. A. Hartley, Description of the Delta of the Danube, 1862 ; Wallace, Auf den Donau von Wien nach Constantinopel,
Vienna, 1864 ; Memoire sur le Régime Administratif établi aux embouchures du Danube, Galatz, 1867 ; Mémoire sur les travaux d'amélioration, 1867 ; Desjardins, Rhone et Danube, Paris, 1870 (a defence of the canalization scheme) ; Sir C. A. Hartley, Description of the Delta of the Danube, 1874 ; Carte du Danube entre Braila et la Mer, Leipsic, 1874, published by the European Commission ; Peters, Die Donau und ihr Gebiet, 1876. (H. A. W.)