The Sieg is a river in North Rhine-Westphalia and Rhineland-Palatinate, Germany. It is a right tributary of the Rhine.The river is named after the Sicambri. It is 155 kilometres (96 mi) in length.The source is located in the Rothaargebirge mountains. From here the river runs southwestwards to the city of Siegen and the hills of Siegerland, both named after the river.