<P> From west to east, the region includes the cities of Duisburg, Oberhausen, Bottrop, Mülheim an der Ruhr, Essen, Gelsenkirchen, Bochum, Herne, Hagen, Dortmund, and Hamm, as well as parts of the more "rural" districts of Wesel, Recklinghausen, Unna and Ennepe - Ruhr - Kreis . The most populous cities are Dortmund (approx . 600,000), Essen (approx. 590,000) and Duisburg (approx . 500,000). The Ruhr area has no administrative center; each city in the area has its own administration, although there exists the supracommunal "Regionalverband Ruhr" institution in Essen . Historically, the western Ruhr towns, such as Duisburg and Essen, belonged to the historic region of the Rhineland, whereas the eastern part of the Ruhr, including Gelsenkirchen, Bochum, Dortmund and Hamm, were part of the region of Westphalia . Since the 19th century, these districts have grown together into a large complex with a vast industrial landscape, inhabited by some 7.3 million people (including Düsseldorf and Wuppertal). </P> <P> For 2010, the Ruhr region was one of the European Capitals of Culture . </P> <P> The urban landscape of the Ruhr extends from the Lower Rhine Basin east to the Westphalian Plain and south to the hills of the Rhenish Massif . Through the centre of the Ruhr runs a segment of the loess belt that extends across Germany from west to east . Historically, this loess belt has underlain some of Germany's richest agricultural regions . </P> <P> Geologically, the region is defined by coal - bearing layers from the upper Carboniferous period . The coal seams reach the surface in a strip along the River Ruhr and dip downward from the river to the north . Beneath the River Lippe, the coal seams lie at a depth of 600 to 800 metres (2,000 to 2,600 feet). The thickness of the coal layers ranges from one to three metres (three to ten feet). This geological feature played a decisive role in the development of coal mining in the Ruhr . </P>

How is the rhine used by the industries of the region