August 13, 1961, the GDR began to block off East Berlin and the GDR from West Berlin by means of barbed wire and antitank obstacles. Streets were torn up, and barricades of paving stones were erected. Tanks gathered at crucial places. The subway and local railway services between East and West Berlin were interrupted. Inhabitants of East Berlin and the GDR were no longer allowed to enter West Berlin, including 60,000 commuters who had been work in West Berlin. In the following days, construction brigades began replacing the provisional barriers with a solid wall.