The German national anthem Deutschlandlied was written in 1841, giving four water bodies as borders of the German language Sprachraum of the time "Von der Maas bis an die Memel, von der Etsch bis an den Belt". This maps outlines them, and the border of the German Confederation of the time.
like _ from http://www.ieg-maps.uni-mainz.de, and: File:Deutscher Bund.png, File:Historisches deutsches Sprachgebiet.PNG, File:Continental West Germanic languages.png
Mueck / derivative work Maximilian Dörrbecker (Chumwa)