The Rhine is one of the longest and most important rivers 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 name of the Rhine derives from Gaulish Renos, and ultimately from the Proto-Indo-European root *reie- ("to move, flow, run"), which is also the root of words like river and run. The Reno River in Italy shares the same etymology. The spelling with -h- seems to be borrowed from the Greek form of the name, Rhenos, seen also in rheos, stream, and rhein, to flow.

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.

Geography

Switzerland, Liechtenstein, Austria, Germany

The Rhine originates at the confluence of the Vorderrhein and Hinterrhein, near Reichenau, Switzerland.
The Vorderrhein, or Anterior Rhine, springs from Lai da Tuma (Tomasee), near the Oberalp Pass and passes the impressive Ruinaulta or Swiss Grand Canyon.
The Hinterrhein, or Posterior Rhine, starts from the Paradies Glacier, near the Rheinquellhorn at the southern border of Switzerland. One of its tributaries, the Reno di Lei, is fed by the Lago di Lei reservoir that drains the Valle di Lei in Italy.

From Reichenau, the Rhine flows north as the Alpenrhein, passes Chur, and forms the border between Liechtenstein and then Austria, on the east side and Canton of St. Gallen of Switzerland, on the west side; then empties into Lake Constance. It emerges from Lake Constance, flows generally westward, as the Hochrhein, passes the Rhine Falls, and is joined by the river Aar. The Aar more than doubles the Rhine's water discharge, to an average of nearly 1,000 m3/s (35,000 cu ft/s). The Aar also contains the waters from the 4,274 m (14,022 ft) summit of Finsteraarhorn, the highest point of the Rhine basin. The Rhine roughly forms the boundary with Germany from Lake Constance, until it turns north at the so-called Rhine knee at Basel.

The Oder is a river in Central Europe. It rises in the Czech Republic and flows through western Poland, later forming 187 kilometres (116 mi) of the border between Poland and Germany, part of the Oder-Neisse line. The river ultimately flows into the Szczecin Lagoon north of Szczecin and then into three branches (the Dziwna, Świna and Peene) that empty into the Baltic Sea.

Names
The Oder is known by several names in different languages: (English and German: Oder; Czech, Slovak and Polish: Odra; Hungarian: Odera; Classical Latin: Viadrus, Viadua; Medieval Latin: Od(d)era).

Geography
The Oder is 854 km long: 112 in the Czech Republic, 742 in Poland (including 187 on the border between Germany and Poland) and is the second longest river in Poland (after the Vistula). It drains 118,861 km² of watershed, 106,056 of which are in Poland (89%), 7,217 in the Czech Republic (6%), and 5,587 in Germany (5%). Channels connect it to the Havel, Spree, Vistula system and Kłodnica. It flows through Silesian, Opole, Lower Silesian, Lubusz, and West Pomeranian voivodeships of Poland and the states of Brandenburg and Mecklenburg-Vorpommern in Germany.

The main branch empties into the Szczecin Lagoon near Police. The Szczecin Lagoon is bordered on the north by islands of Usedom (west) and Wolin (east). Between these two islands, there is only a narrow channel (Świna) going to the Bay of Pomerania, which forms a part of the Baltic Sea.

The largest city on the Oder River is Wrocław.