The Danube is a truly European river. It measures 2,888 kilometers (nearly 1,800 miles) from its source in the Black Forest to its mouth in the Black Sea, and it connects 10 countries with very different cultures. The Danube is therefore not only the second-longest European river after the Volga, but also the most international river in the world. It was and is one of the most important trade routes in Europe and forms a lifeline for many people.