In the tucked away Black Forest town of Donaueschingen, the mighty River Danube begins. It rises as a clear, three metre-deep wellspring in the town centre, encircled by a stone basin sculpted with zodiac symbols. From there, the Danube – Donau in German – flows full tilt onwards for 1,771 miles to its mouth on the Black Sea, passing through the great cities of Vienna, Budapest and Belgrade.