In Mainz, the Main flows into the Rhine. This 524 km long river is the longest of the right bank Rhine tributaries.
It is unusual for Middle European rivers to flow from east to west, as does the Main, along several low mountain ranges, small historic towns, the striking outline of Würzburg and the wine-growing area of Franconia. In its upper course, the R. Main has largely preserved its natural character. About 30 km upstream its confluence with the Rhine it flows through the centre of Frankfurt.
that the Main-Danube canal connects the Rhine with the Danube?
Thus ships may cross Europe on their way from the North Sea to the Black Sea.