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Duisburg (German pronunciation: [ˈdyːsbʊɐ̯k] ( listen)) is a city in North Rhine-Westphalia , Germany . The world 's biggest inland port , it is also close to Düsseldorf Airport . In the early Middle Ages it was a royal court of the Franks, first mentioned in writing in 883. Duisburg is a result of numerous incorporations of surrounding towns and smaller cities . It is the fifteenth-largest city in Germany and the fifth-largest city in North Rhine-Westphalia , with 486,855 residents at the end of 2013. It is the central city of the Rhine-Ruhr metropolitan area . The city is renowned for its steel industry . All blast furnaces in the Ruhr are now located in Duisburg. In 2000 , 49% of all hot metal and 34.4% of all pig iron in Germany was produced here. It also has a large brewery, König.