Mureş River, river, rising in the Giurgeu Range in the Eastern Carpathian Mountains, east-central Romania. It cuts a gorge between the Căliman and Gurghiu ranges, crosses the Transylvanian Basin southwestward, and then cuts across the Western Carpathians between the Poiana Ruscăi and the Bihoru mountains and emerges onto the Tisa Plain to join the Tisa (Tisza) River at Szeged, Hung., after a course of about 450 miles (725 km). The Mureş is the most important tributary of the Tisa with respect to quantity of water. The large area of its basin, its length, and its diagonal cut across the Transylvanian Basin make it a significant traffic route. The river is navigable for small craft below Deva and is followed by road and rail arteries; several important cities and towns lie along its course.