Danube is the longest international river in Europe. It flows trough Germany, Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldavia and Ukraine. Its spring is in Schwarzwald (“the black forest”) and it mouths into the Black Sea. It is 2.850 km long, the navigable part is 2.414 km.
Danube is in the center of the European network of navigable inland waterways. After the Main-Danube connection was created, Danube became a part of the trans-European waterway linking seaports at the North Sea (Rotterdam, Amsterdam) and at the Black Sea (Constanca) – 3.505 km long. An example to show the great importance of the Rhine-Mine-Danube waterway: the first attempt to connect Rhine and Danube was made as early as in 793. Charlemagne, the Frankish emperor, started a canal construction to link the two rivers. Works were soon suspended, but remnants of a canal, near Graben in Bavaria, witness them. The idea came to life only 12 centuries later.
There are also other ideas for linking Danube with other rivers and trough them to other seas, e.g. Adriatic Sea, Aegean Sea.
The region of middle Danube spans from Hungary to Romania. It is here that the Danube meets its major tributaries: Drava, Tisa, Tamiš, Sava, Velika Morava, Nera, Mlava, Pek and Porečka reka. The confluence of these rivers collects waters from an area of about 620.000 km² and the theritory of many danubian countries. This wast area is rich in all kinds of natural resources: strong winds, fresh-water, fertile lands and rich ore-, coal, oil and gas deposits.