Danube
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. The Danube then flows southeast for about , passing through four capital cities (Vienna, Bratislava, Budapest and Belgrade) before emptying into the Black Sea via the Danube Delta in Romania and Ukraine.
Abnoba
The Danube begins with two small rivers draining the Black Forest: the Breg and the Brigach, both Celtic names. The longest is the most favorable candidate: the Breg. The Abnobaei montes would therefore be the Baar foothills of the Swabian Alb near Furtwangen im Schwarzwald.