The Danube is a river in Central Europe, the continent's second longest after the Volga. Classified as an international waterway, it originates in the town of Donaueschingen which is in the Black Forest of Germany at the confluence of the rivers Brigach and Breg. The Danube then flows southeast for 2,872 km (1,785 mi), passing through four Central European capitals before emptying into the Black Sea via the Danube Delta in Romania and Ukraine.
Once a long-standing frontier of the Roman Empire, the river passes through or touches the borders of ten countries: Romania (29.0% of basin area), Hungary (11.6%), Serbia (10.2%), Austria (10.0%), Germany (7.0%), Slovakia (5.9%), Bulgaria (5.9%), Croatia (4.4%), Ukraine (3.8%), and Moldova (1.6%), more than any other. Its drainage basin extends into nine more.
The Danube Delta has been a UNESCO World Heritage Site since 1991. Its wetlands (on the Ramsar list of wetlands of international importance) support vast flocks of migratory birds, including the endangered Pygmy Cormorant (Phalacrocorax pygmaeus). Rival canalization and drainage schemes threaten the delta: see Bastroe Channel. The Danube Delta is the second largest river delta in Europe, after the Volga Delta, and is the best preserved on the continent. The greater part of the Danube Delta lies in Romania (Tulcea county), while its northern part, on the left bank of the Chilia arm, is situated in Ukraine (Odessa Oblast).
The approximate surface is 4152 km², of which 3446 km² are in Romania. If one includes the lagoons of Razim-Sinoe (1015 km² of which 865 km² water surface), which are located south of the delta proper, but are related to it geologically and ecologically (their combined territory is part of the World Heritage Site), the total area of the Danube Delta reaches 5165 km². The waters of the Danube, which flow into the Black Sea, form the largest and best preserved of Europe's deltas. The Danube delta hosts over 300 species of birds as well as 45 freshwater fish species in its numerous lakes and marshes.
Although the headwaters of the Danube are relatively small today, geologically, the Danube is much older than the Rhine, with which its catchment area competes in today's southern Germany. This has a few interesting geological complications. Since the Rhine is the only river rising in the Alps mountains which flows north towards the North Sea, an invisible line beginning at Piz Lunghin divides large parts of southern Germany, which is sometimes referred to as the European Watershed.
Before the last ice age in the Pleistocene, the Rhine started at the southwestern tip of the Black Forest, while the waters from the Alps that today feed the Rhine were carried east by the so-called Urdonau (original Danube). Parts of this ancient river's bed, which was much larger than today's Danube, can still be seen in (now waterless) canyons in today's landscape of the Swabian Alb. After the Upper Rhine valley had been eroded, most waters from the Alps changed their direction and began feeding the Rhine. Today's upper Danube is but a meek reflection of the ancient one.
The Danube basin was the site of some of the earliest human cultures. The Danubian Neolithic cultures include the Linear Pottery cultures of the mid-Danube basin. Many sites of the sixth-to-third millennium BC Vinca culture, (Vinca, Serbia) are sited along the Danube. The third millennium BC Vucedol culture (from the Vucedol site near Vukovar, Croatia) is famous for its ceramics. The river was part of the Roman Empire's Limes Germanicus. The Romans often used the river Danube as a northern border for their empire. Alexander the Great defeated the Triballian king Syrmus and the northern barbarian Thracian and Illyrian tribes by advancing from Macedonia as far as the Danube in 336BC.
Important tourist and natural spots along the Danube include the Wachau Valley, the Nationalpark Donau-Auen in Austria, Gemenc in Hungary, the Naturpark Obere Donau in Germany, Kopacki rit in Croatia, Iron Gate in Serbia and Romania, the Danube Delta in Romania, and the Srebarna Nature Reserve in Bulgaria. The Danube Banks in Budapest are a part of Unesco World Heritage sites, they can be viewed from a number of sightseeing cruises offered in the city.
The Danube Bend is also a popular tourist destination.
In addition to the bordering countries (see above), the drainage basin includes parts of nine more countries: Bosnia and Herzegovina (4.6%), the Czech Republic (2.9%), Slovenia (2.0%), Montenegro (0.9%), Switzerland (0.2%), Italy (<0.1%), Poland (<0.1%), the Republic of Macedonia (<0.1%) and Albania (<0.1%). The highest point of the drainage basin is the summit of Piz Bernina at the Italy–Switzerland border, 4,049 metres (13,284 ft).
The Danube's watershed extends into many other countries. Many Danubian tributaries are important rivers in their own right, navigable by barges and other shallow-draught boats. From its source to its outlet into the Black Sea, its main tributaries are (in order that they enter):
- Iller (entering at Ulm)
- Naab (entering at Regensburg)
- Regen (entering at Regensburg)
- Inn (entering at Passau)
- Morava (entering near Devín Castle)
- Váh (entering at Komárno)
- Vuka (entering at Vukovar)