Duisburg is a German city in the western part of the Ruhr Area (Ruhrgebiet) in North Rhine-Westphalia. It is an independent metropolitan borough within Regierungsbezirk Düsseldorf. With the world's biggest inland harbor and its proximity to Düsseldorf Airport, Duisburg has become an important venue for commerce and steel production. In the early Middle Ages it was a royal court of the Franks, first mentioned in writing in 883.