The Rhine (German: Rhein; Dutch: Rijn; French: Rhin) is a European river that runs from the Swiss canton of Grisons in the southeastern Swiss Alps through Germany and eventually flows into the North Sea coast in the Netherlands and is the twelfth longest river in Europe, at about 1,233 km (766 mi), with an average discharge of more than 2,000 m³/s (71,000 cu ft/s).

The Rhine and the Danube formed most of the northern inland frontier of the Roman Empire and, since those days, the Rhine has been a vital and navigable waterway carrying trade and goods deep inland. It has also served as a defensive feature and has been the basis for regional and international borders. The many castles and prehistoric fortifications along the Rhine testify to its importance as a waterway. River traffic could be stopped at these locations, usually for the purpose of collecting tolls, by the state that controlled that portion of the river.