 The Ruhr first passes the towns of Meschede, Arnsberg, Wickede, Fröndenberg, Holzwickede, Iserlohn, and Schwerte.Then the river marks the southern limit of the Ruhr area, passing Hagen, Dortmund, Herdecke, Wetter, Witten, Bochum, Hattingen, Essen, Mülheim, and Duisburg.The Ruhr area was Germany's primary industrial area during the early- to mid-20th century.