THE DANUBE RIVER IS the longest river in western Europe, surpassed in Europe as a whole only by the VOLGA in RUSSIA. Fourteen countries are drained by its watershed, covering over 312,000 square mi (800,000 square km): GERMANY, AUSTRIA (and small parts of eastern SWITZERLAND), the CZECH REPUBLIC, SLOVAKIA, HUNGARY (and a small corner of southwest UKRAINE), SLOVENIA, CROATIA, BOSNIA AND HERZEGOVINA, SERBIA AND MONTENEGRO, BULGARIA, ROMANIA, and MOLDOVA. The river travels 1,760 mi (2,850 km) from its source in Germany's Black Forest to its large delta on the BLACK SEA, passing through some of the most beautiful and historic cities in Europe, including Vienna, Budapest, and Belgrade. The most famous stretch of the river, between Vienna and Budapest, has been immortalized numerous times in paintings, poetry, and music, notably Johann Strauss, Jr.'s “An der schonen, blauen Donau” (“On the Beautiful, Blue Danube”).
The Greeks called the Danube the “Ister,” the “Greatest of Rivers,” and for many centuries it was the border between the civilized Greco-Roman world and the Germanic barbarians to the north. Many centuries later, it formed the center, not the boundary, of the multiethnic Habsburg Empire, centered on Vienna and Budapest, which was torn apart by the peace settlements after World War I and by the Iron Curtain of the post-World War II era. There remains, however, some desire to reunite much of the region into a Danubian economic confederation, reflecting the reality that although language and culture divide Austrians, Hungarians, Serbs, Bulgarians and Romanians, the river unites them through commerce and industry.
The Danube starts in southwestern Germany, where it is called the Donau. Two small rivers, the Brege and the Brigach, come together at Donaueschingen, a town in the Black Forest. Its springs lie only a few meters from streams that flow westward into the Rhine watershed, thus ending up in the North Sea rather than the Black Sea, nearly 1,000 miles (3,000 km) apart. In fact, porous rocks in this area result in much of the water of the upper Danube actually seeping through the rocks to join the Rhine watershed, which has a lower elevation.
The river is too small for navigation as it winds through the Swabian Alps, passing castles and monasteries, and the ancient German cities of Ulm and Regensburg, once the capital of the Holy Roman Empire. At Passau, on the border with Austria, the Danube is joined by its first large tributary, the Inn. This was historically the western terminus of commercial river traffic, especially for grain coming to Central Europe from the plains of Hungary, but also for coal and iron ore from as far away as Russia.
In Upper Austria, the Danube passes some of the most famous baroque buildings in Europe, especially Melk, the Versailles of monasteries, perched on a hill above the river valley. Finally the river broadens into the famously smooth (and generally muddy brown, not blue) Danube as it passes by the capital cities of Vienna, Bratislava, and Budapest before turning south to cross the broad Hungarian Plain. This plain, the breadbasket of Central Europe, was also the site of many important battles, from the defeat and forced settling of the Hungarian people by Emperor Otto I in 955, to the destruction of the native Hungarian kingdom by the Turks at Mohacs in 1526, and the defeat of Turkish forces after the siege of Vienna in 1683, finally halting their progress toward Central Europe.
South of this plain, the river again enters mountainous regions, guarded by the fortress city of Belgrade. In these middle reaches, the river (called Duna in Hungarian and Dunav in Serbian) receives its largest tributaries, the Tisza, which drains the eastern Hungarian Plain, the historic region of Transylvania (northwestern Romania), and southwestern Ukraine; and the Drava and Sava, which receive most of the waters of Slovenia, Croatia and Bosnia and Herzegovina.
In Serbia, the river's course meanders as it cuts passages through the confluence of the easternmost ALPS and the Carpathian Mountains. At its narrowest, the river passes through the Iron Gates, the site of one of Europe's largest hydroelectric projects, the Djerdap, which provides almost half of the electricity consumed by Serbia and Romania. The other major hydroelectric project on the Danube is the Gabcikovo dam, in Slovakia. This dam, built in 1992, created a huge 11-mi (24 km) reservoir, with serious ecological consequences downstream in Hungary. Originally a partner in the project, Hungary withdrew with the fall of communism, causing severe tensions with the Slovak government. Other man-made projects along the river's course include the Rhein-Main-Donau Kanal, built in 1992, which links the North Sea to the Black Sea, though it is still mostly underused.
The lower course of the Danube forms the border between Bulgaria and Romania, through a broad drainage basin between the Carpathian and Balkan mountain ranges to the north and south. The river ends in a vast DELTA in Romania, the largest in Europe, with an area of 1,700 square mi (4,345 square km). Part of the delta also lies in the Ukraine. Flow at the mouth of the Danube averages 229,450 cubic ft (6,500 cubic m) per second, but has been recorded at 10 times this volume during high flooding. Some 122 million tons of sediment is discharged each year, creating one of the most extensive and fertile wetlands on Earth. Most of this is now protected by the Danube Delta Biosphere Reserve, 1.7 million acres (679,222 hectares) of marshes and lakes, declared a UNESCO World Heritage site in 1991.
The Romanian city of Galati, where the last major Danubian tributary, the Prut, enters the basin from Moldova to the north, is the river's chief port for oceangoing vessels, although it is 90 mi (145 km) from the Black Sea. Ships traverse the largest of the three main Danube channels (the Sfintu Gheorghe) to enter the Black Sea, and thus to the Mediterranean. It is estimated that 100 million tons of cargo are transported each year on the Danube as a whole, underlying the economic importance of this waterway to much of Central and Eastern Europe.