 The most important towns of the region from Duisburg to the imperial city of Dortmund were concentrated along the Hellweg from the Rhineland to Westphalia.Since the 19th century, these cities have grown together into a large complex with a vast industrial landscape, inhabited by some 7.3 million people (including Düsseldorf and Wuppertal, large cities that are nearby but officially not part of the Ruhr area).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.