Source of the Danube
As early as 1847 the following definition can already be found in the "Universallexikon des Großherzogtums Baden" (Universal Lexicon of the Grand Duchy of Baden): “Danube, the biggest river of Germany, rises at the Martinskapelle in a wild and lonely area of the Black Forest, is called Brege at its origin and forms the river Danube in Donaueschingen where it is unified with the Brigach." (German original: „Donau, der größte Fluß Deutschlands, entspringt bei der Martinskapelle in einer wilden und einsamen Gegend des Schwarzwaldes, heißt am Anfang Brege… und bildet erst in Donaueschingen, wo sie sich mit der Brigach vereinigt, die Donau.“)
Danu (Irish goddess)
The etymology of the name has been a matter of much debate since the 19th century, with some earlier scholars favoring a link with the Vedic water goddess Danu, whose name is derived from the Proto-Indo-European root "*dʰenh₂-" "to run, to flow", which may also lie behind the ancient name for the river Danube, "Danuuius" – perhaps of Celtic origin, though it is also possible that it is an early Scythian loanword in Celtic.