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 1,914 km (1,189 mi), passing through five capital cities 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 and its drainage basin extends into nine more.
Leisure and travel cruises on the river are of great significance. Besides the often frequented route between Vienna and Budapest, some ships even go from Passau in Germany to the Danube Delta and back. During the peak season, more than 70 cruise liners are in use on the river, while the traffic-free upper parts can only be discovered with canoes or boats. The Danube region is not only culturally and historically of importance, but also due to its fascinating landmarks and sights important for the regional tourism industry. With its well established infrastructure regarding cycling, hiking and travel possibilities, the region along the Danube attracts every year an international clientele.
Along its course, the Danube is a source of drinking water for about twenty million people. In Baden-Württemberg, Germany, almost thirty percent (as of 2004) of the water for the area between Stuttgart, Bad Mergentheim, Aalen and Alb-Donau (district) comes from purified water of the Danube. Other cities such as Ulm and Passau also use some water from the Danube. In Austria and Hungary, most water is drawn from ground and spring sources, and only in rare cases is water from the Danube used. Most states also find it too difficult to clean the water because of extensive pollution; only parts of Romania where the water is cleaner still obtain drinking water from the Danube on a regular basis.
The Route of Emperors and Kings is an international touristic route leading from Regensburg to Budapest, calling in Passau, Linz and Vienna. 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. In medieval Regensburg, with its maintained old town, stone bridge and cathedral, the Route of Emperors and Kings begins. Before the Route of Emperors and Kings ends in Budapest, you pass Bratislava and Vienna, the latter which was seen as the twin town of Budapest during the times of the Austro-Hungarian Empire. Since ancient Roman times, famous emperors and their retinue travelled on and along the Danube and used the river for travel and transportation. While travelling on the mainland was quite exhausting, most people preferred to travel by ship on the Danube. So the Route of Emperors and Kings was the setting for many important historical events, which characterize the Danube up until today.