Moselle River, German Mosel, river, a west-bank tributary of the Rhine River, flowing for 339 miles (545 km) across northeastern France and western Germany. Rising on the forested slopes of the Vosges massif, the river meanders past Épinal, Pont-Saint-Vincent, Toul, Frouard, Metz, and Thionville before leaving France to form the frontier between Germany and Luxembourg for a short distance. The river enters Germany and flows past Trier to its confluence with the Rhine at Koblenz. In this sector of the valley (German: Moseltal) are the vineyards from which the famous Moselle wines are produced. The Moselle River’s chief tributaries are the Madon, Orne, and Sauer (French: Sûre) on the west and the Meurthe, Seille, and Saar (French: Sarre) on the east. Above Metz the Moselle has been navigable to 300-ton barges since the 19th century. It connects at Toul and Frouard with the Rhine-Marne Canal.