Essen (.mw-parser-output .IPA-label-small{font-size:85%}.mw-parser-output .references .IPA-label-small,.mw-parser-output .infobox .IPA-label-small,.mw-parser-output .navbox .IPA-label-small{font-size:100%}German pronunciation: [ˈɛsn̩] ⓘ) is the central and, after Dortmund, second-largest city of the Ruhr, the largest urban area in Germany. Its population of 586,608 makes it the fourth-largest city of North Rhine-Westphalia after Cologne, Düsseldorf and Dortmund, as well as the ninth-largest city of Germany. Essen lies in the larger Rhine-Ruhr metropolitan region, second largest by GDP in the EU, and is part of the cultural area of Rhineland. Because of its central location in the Ruhr, Essen is often regarded as the Ruhr's "secret capital".[3] Two rivers flow through the city: the Emscher in the north, and in the south the Ruhr River, which is dammed in Essen to form the Lake Baldeney (Baldeneysee [de]) and Lake Kettwig (Kettwiger See [de]) reservoirs. The central and northern boroughs of Essen historically belong to the Low German (Westphalian) language area, and the south of the city to the Low Franconian Bergish area. Essen is seat to several of the region's authorities, as well as to eight of the 100 largest publicly held German corporations by revenue, including three DAX-listed corporations. Essen is often considered the energy capital of Germany with E.ON and RWE, Germany's largest energy providers, both headquartered in the city. Essen is also known for its impact on the arts through the respected Folkwang University of the Arts, its Zollverein School of Management and Design, and the Red Dot industrial product design award. In early 2003, the universities of Essen and the nearby city of Duisburg (both established in 1972) were merged into the University of Duisburg-Essen with campuses in both cities and a university hospital in Essen. In 1958, Essen was chosen as the seat to the Roman Catholic Diocese of Essen (often referred to as Ruhrbistum (diocese of the Ruhr).