Vennbahn

thumb|right|Vennbahn Map showing current Belgium–Germany border|Belgian-German border. The pre-1958 border southeast of Roetgen differed. The '''''' (, "Fen Railway") is a former railway line that was built partly across what was then German territory by the Prussian state railways. It is now entirely in Belgium, because the trackbed of the line, as well as the stations and other installations, were made provisional Belgian territory in 1919 (permanent in 1922) under an article of the Treaty of Versailles.

This created six small exclaves of Germany on the line's western side, of which five remain. The treaty (not the location of the trackbed, per se) also created one small Belgian counter-enclave, a traffic island inside a three-way German road intersection near which lasted until 1949.