Duisburg 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. The University of Duisburg-Essen, with 39,000 students, ranks among the ten largest German universities.GeographyDuisburg is in the Lowland Rhine area at the confluence of the Rhine and Ruhr and near the outskirts of the Bergisches Land. The city spreads along both sides of these rivers.Adjacent citiesThe following cities border Duisburg (clockwise starting from north-east): Oberhausen, Mülheim an der Ruhr, Ratingen, Düsseldorf, Meerbusch, Krefeld, Moers, Rheinberg, and Dinslaken.