Rhine River. The Rhine is one of the major European rivers, which has its sources in Switzerland and flows in a mostly northerly direction through Germany and the Netherlands, emptying into the North Sea. The river begins in the Swiss canton of Graubünden in the southeastern Swiss Alps, forms part of the Swiss-Liechtenstein, Swiss-Austrian, Swiss-German and then the Franco-German border, then flows through the German Rhineland and the Netherlands and eventually empties into the North Sea. The largest city on the Rhine is Cologne, Germany, with a population of more than 1,050,000 people. It is the second-longest river in Central and Western Europe, at about 1,230 km, with an average discharge of about 2,900 m 3 /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.Its importance as a waterway in the Holy Roman Empire is supported by the many castles and fortifications built along it. In the modern era, it has become a symbol of German nationalism. Among the biggest and most important cities on the Rhine are Cologne, Düsseldorf, Rotterdam, Strasbourg and Basel. The variants of the name of the Rhine in modern languages are all derived from the Gaulish name Renos, which was adapted in Roman-era geography as Greek, Latin Rhenus. Spanish is with French in adopting the Germanic vocalism Rin-, while Italian, Occitan and Portuguese retain the Latin Ren-. The Gaulish name Renos belongs to a class of river names built from the PIE root to move, flow, run, also found in other names such as the Reno in Italy. The grammatical gender of the Celtic name is masculine, and the name remains masculine in German, Dutch and French. The Old English river name was variously inflected as masculine or feminine; and its Old Icelandic adoption was inflected as feminine. The length of the Rhine is conventionally measured in Rhine-kilometers, a scale introduced in 1939 which runs from the Old Rhine Bridge at Constance to Hoek van Holland. The river is significantly shortened from its natural course due to a number of canalisation projects completed in the 19th and 20th century. The total length of the Rhine, to the inclusion of Lake Constance and the Alpine Rhine is more difficult to measure objectively; it was cited as 1,232 kilometres by the Dutch Rijkswaterstaat in 2010.