“Hinc movet Euphrates, illinc Germania bellum”. – Virgil, Georgic I, l. 509.
“Here the Euphrates, there Germany wages war.” Americans might see their last century partly in those terms.
Virgil was writing about the time of the confrontation of Octavian and Mark Antony at Actium.
The North Sea is connected with the Black Sea via the Main-Danube canal in Bavaria (the Main being a tributary of the Rhine), which was opened in its present form in 1992. It replaced the Ludwig Canal.
The Kara Su or Western Euphrates, one of the Euphrates’ two sources (the other is the Murat Su or Eastern Euphrates), rises in northeastern Turkey only sixty miles from the southeastern corner of the Black Sea. Kara means black. (Murat is a proper name.) So only a sixty-mile portage separates the Gulf from the North Sea.
The Tigris also rises in Turkey, a little further south.
A Study of History, Vol IV, OUP, 1939 (footnote)