Essen is a large city in the centre of the Ruhr area and the Rhine-Ruhr metropolitan region. After Cologne, Düsseldorf and Dortmund, Essen is the fourth largest city in the state of North Rhine-Westphalia and one of its major centres. The independent city in the administrative district of Düsseldorf is one of the ten largest cities in Germany with a population of around 580,000. As an important industrial location, Essen is the seat of well-known major companies and is also a university location with the university as a whole, which was founded in 1972 and merged with the university at the neighbouring location in Duisburg in 2003 to form the University of Duisburg-Essen. In 1958, the city became the seat of the newly founded Essen diocese.