North Rhine-Westphalia (German:Nordrhein-Westfalen) [ˈnɔʁtʁaɪ̯n vɛstˈfaːlən], commonly shortened NRW) is the most populous state of Germany, with a population of approximately 18 million, and the fourth largest by area. Its capital is Düsseldorf; the biggest city is Cologne. Four of Germany's ten biggest cities—Cologne, Düsseldorf, Dortmund, and Essen—are located within the state, as well as the biggest metropolitan area of the European continent, Rhine-Ruhr.