adopted the Germanic vocalism , Italian, Occitan, and Portuguese have retained the Latin . The Gaulish name Rēnos (Proto-Celtic or pre-Celtic *Reinos) 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 (as well as of its Greek and Latin adaptation) is masculine, and the name remains masculine in German, Dutch, French, Spanish and Italian. The Old English river name was variously inflected as masculine or feminine; and its Old Icelandic adoption was inflected as feminine. Geography The length of the Rhine is conventionally measured in "Rhine-kilometers" (Rheinkilometer), a scale introduced in 1939 which runs from the Old Rhine Bridge at Constance (0 km) to Hook of Holland (1036.20 km). The river is significantly shortened from its natural course due to a number of canalization 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 by the Dutch Rijkswaterstaat in 2010. Its course is conventionally divided as follows: Headwaters and sources Sources The Rhine carries its name without distinctive accessories only from the confluence of the Rein Anteriur/Vorderrhein and Rein Posteriur/Hinterrhein next to Reichenau in Tamins. Above this point is the extensive catchment of the headwaters of the Rhine. It belongs almost exclusively to the Swiss canton of Graubünden, ranging from Saint-Gotthard Massif in the west via one valley lying in Ticino and Italy in the south to the Flüela Pass in the east. The Rhine is one of the four major rivers taking their source in the Gotthard region, along with the Ticino, Rhône and Reuss. Traditionally, Lake Toma near the Oberalp Pass in the Gotthard region is seen as the source of the Anterior Rhine and the Rhine as a whole. The Posterior Rhine rises in the Rheinwald below the Rheinwaldhorn. Anterior Rhine and Posterior Rhine The source of the river is generally considered north of Lai da Tuma/Tomasee on Rein Anteriur/Vorderrhein, although its southern tributary Rein da Medel is actually longer before its confluence with the Anterior Rhine near Disentis. The Anterior Rhine (, ) springs from Lai da Tuma/Tomasee, near the Oberalp Pass and passes the impressive Ruinaulta formed by the largest visible rock slide in the alps,