Main River), a river in Germany. It flows westward from the Fichtel Mountains, where the Roter Main and Weisser Main join, and empties into the Rhine River. The Main is 307 miles (494 km) long, and is navigable between Bamberg and Mainz (on the Rhine). Other ports include Würzburg and Frankfurt. The Rhine-Main-Danube Canal, completed in 1992, links the Main and Danube rivers between Bamberg and Kelheim, allowing traffic to move between the North and Black seas.