Originating in Germany, the Danube flows southeast for 2,850 km (1,770 mi), passing through or bordering Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova, and Ukraine.

The Danube's longest headstream Breg rises in Furtwangen im Schwarzwald, while the river carries its name from its source confluence in the palace park in Donaueschingen onwards.

The Danube river basin is home to such fish species as pike, zander, huchen, Wels catfish, burbot and tench.

A few species of euryhaline fish, such as European seabass, mullet, and eel, inhabit the Danube Delta and the lower portion of the river.

Today the river carries its name from its source confluence in Donaueschingen, Germany, to its discharge into the Black Sea via the Danube Delta in Romania and Ukraine.

[14] Classified as an international waterway, it originates in the town of Donaueschingen, in the Black Forest of Germany, at the confluence of the rivers Brigach and Breg.

Prut (entering near Galați) The Danube flows through many cities, including four national capitals (shown below in bold), more than any other river in the world.

[39] In 2010–12, shipping companies, especially from Ukraine, claimed that their vessels suffered from "regular pirate attacks" on the Serbian and the Romanian stretches of the Danube.

[40][41][42] However, the transgressions may not be considered acts of piracy, as defined according to the United Nations Convention on the Law of the Sea, but rather instances of "river robbery".

[43] On the other hand, media reports say the crews on transport ships often steal and sell their own cargo and then blame the plundering on "pirates", and the alleged attacks are not piracy but small-time contraband theft along the river.

Its wetlands support vast flocks of migratory birds of over 300 species, including the endangered pygmy cormorant (Phalacrocorax pygmaeus).

[45] The International Commission for the Protection of the Danube River (ICPDR) is an organization that consists of 14 member states (Germany, Austria, the Czech Republic, Slovakia, Slovenia, Hungary, Croatia, Bosnia and Herzegovina, Serbia, Bulgaria, Romania, Moldova, Montenegro, and Ukraine) and the European Union.

Members include representatives from Austria, Bulgaria, Croatia, Germany, Hungary, Moldova, Slovakia, Romania, Russia, Ukraine, and Serbia; it meets regularly twice a year.

The commission dates to the Paris Conferences of 1856 and 1921, which established for the first time an international regime to safeguard free navigation on the Danube.

Most of this water resurfaces only 12 km (7.5 mi) south at the Aachtopf, Germany's wellspring with the highest flow, an average of 8,500 L/s (300 cu ft/s), north of Lake Constance—thus feeding the Rhine.

Since such large volumes of underground water erode much of the surrounding limestone, it is estimated that the Danube upper course will one day disappear entirely in favor of the Rhine, an event called stream capturing.

Darius the Great, king of Persia, crossed the river in the late 6th century BCE to invade European Scythia and to subdue the Scythians.

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 336 BCE.

The crossing of the Danube into Dacia was achieved by the Imperium Romanum, first in two battles in 102 and then in 106 after the construction of a bridge in 101 near the garrison town of Drobeta at the Iron Gate.

The lower Danube was also called the Keras Okeanoio (Gulf or Horn of Okeanos) in the Argonautica by Apollonius Rhodos (Argon.

At the end of the Okeanos Potamos, is the holy island of Alba (Leuke, Pytho Nisi, Isle of Snakes), sacred to the Pelasgian (and later, Greek) Apollo, greeting the sun rising in the east.

[51] In the 19th century, the Danube was an important waterway but was, as The Times of London put it, "annually swept by ice that will lift a large ship out of the water or cut her in two as if she were a carrot.

However, some of the river's resources have been managed in an environmentally unsustainable manner in the past, leading to damage by pollution, alterations to the channel, and major infrastructure development, including large hydropower dams.

[53] The sturgeon stocks associated with the Danube River basin have, over the centuries, formed the basis of a large and significant commercial fishery, renowned throughout the world.

[59] 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, Kopački rit in Croatia, Iron Gate in Serbia and Romania, the Danube Delta in Romania, and the Srebarna Nature Reserve in Bulgaria.

With its well established infrastructure regarding cycling, hiking, and travel possibilities, the region along the Danube attracts every year an international clientele.

[60] 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.

[63] The international consortium ARGE Die Donau-Straße der Kaiser und Könige, comprising ten tourism organisations, shipping companies, and cities, strives for the conservation and touristic development of the Danube region.

Before the Route of Emperors and Kings ends, you pass Bratislava and Budapest, the latter of which was seen as the twin town of Vienna during the times of the Austro-Hungarian Empire.

The route got its name from the Holy Roman Emperor Frederick I of Barbarossa and the crusaders as well as from Richard I of England who had been jailed in the Dürnstein Castle, which is situated above the Danube.