Danube (ancient Danubius, and in the lower part of its course, Ister; German Donau; Slovak Dunaj; Hungarian Duna; Serbo-Croatian and Bulgarian Dunav; Romanian Dunărea; Ukrainian Dunay), second longest river in Europe, and one of the principal transportation arteries on the continent. It is the only major European river to flow from west to east. It rises in the Black Forest region of Germany and flows in a generally easterly direction for a distance of about 2850 km (1770 mi), emptying, on the Romanian coast, into the Black Sea. The delta of the Danube is a region of desolate marshes and swamps, broken by tree-covered elevations. The Danube is navigable by ocean vessels to Brăila, Romania, and by river craft as far as Ulm in Germany, a distance of 2,600 km (1,600 mi). About 60 of the approximately 300 tributaries of the Danube are navigable. The principal ones, in the order in which they merge with the Danube, include the Lech, Isar, Inn, Morava, Váh, Raab (Rába), Drava (Drau), Tisza, Sava, Siret, and Prut. The Danube basin, more than 777,000 sq km (more than 300,000 sq mi) in area, includes parts of Germany, Austria, Slovakia, Hungary, Serbia and Montenegro, Croatia, Bosnia and Herzegovina, Slovenia, Bulgaria, Romania, and Ukraine. Important cities on the river include Ulm, Regensburg, and Passau, in Germany; Linz and Vienna, in Austria; Bratislava, Slovakia; Budapest, Hungary; Belgrade, Serbia; and Galaţi and Brăila, in Romania. Canals link the Danube to the Main, Rhine, and Odra (Oder) rivers, providing a commercial route between the Black and North seas. The Danube Valley between Linz and Vienna, Austria, is noted for its beautiful scenery.
Several countries have built dams and hydroelectric power plants on the Danube. In the early 1970s the Iron Gate hydroelectric project was completed as a joint effort between the governments of Romania and the former Yugoslavia. Located at the Iron Gate gorge on the border of Romania and Serbia (which inherited Yugoslavia’s portion of the project when that country dissolved in 1991 and 1992), the project includes a dam and two power plants. The construction of the Gabčíkovo dam, located in southern Slovakia, began in the 1980s and was completed in late 1992.
The Danube has always been an important route between western Europe and the Black Sea. It formed, in the 3rd century ad, the northern boundary of the Roman Empire in southeastern Europe. Early in the Middle Ages Goths, Huns, Avars, Slavs, Magyars, and other migratory peoples crossed the Danube on their way to invade the Roman, and later the Byzantine, Empire. It served as an artery for the Crusaders into Byzantium (Constantinople) and from there to the Holy Land; later it eased the advancement (beginning at the end of the 14th century) of the Ottomans into western and central Europe. In the 19th century it became an essential link between the growing industrial centers of Germany and the agricultural areas of the Balkan Peninsula. At that time, most of the river’s middle and upper course lay within the Austrian Empire; the lower part belonged to the decaying Ottoman Empire. As Ottoman control over the Balkans weakened, Austria and the other European powers moved to prevent Russia from acquiring the strategic Danube delta.
By the terms of the Treaty of Paris (1856), which ended the Crimean War, a European commission was established to control the delta. The commission made a number of changes in the delta and in the lower reaches of the river beneficial to navigation. The Treaty of Versailles (1919), concluding World War I, confirmed the European commission, and set up another one to control the Danube above the delta. During World War II (1939-1945) the commissions were abolished by Nazi Germany, which controlled all of the river from 1940 to 1944. After the war the Communist-bloc nations bordering the river formed a new Danube Commission, headquartered at Budapest. Austria was admitted in 1960 and West Germany in 1963.
In the late 1970s the Czechoslovak and Hungarian governments launched the Gabčíkovo-Nagymaros hydroelectric project on the section of the Danube that formed the boundary between the two countries. The project called for the construction of two major dams, one at Nagymaros in Hungary, and the other at Gabčíkovo in eastern Czechoslovakia (now Slovakia). However, in 1989 Hungary abandoned the project, claiming that the dams and the network of canals and reservoirs surrounding them would change the flow of the river and thus damage the surrounding environment. Czechoslovakia proceeded with the construction of the Gabčíkovo dam, despite angry protests from the Hungarian government, which demanded that the international boundary between the two countries be redrawn to reflect the Danube’s northward shift. Slovakia inherited the dispute when it became an independent country in January 1993. That year, the Slovak and Hungarian governments referred the dispute to the International Court of Justice at The Hague, Netherlands, for mediation. In 1997 the court ruled that both countries had violated the original hydroelectric project agreement and ordered them to compensate one another and continue negotiations.