On August 13, 1961, Ulbricht had ordered barbed wire between East and West Berlin. The barbed wire was later changed to cement walls. This prevented the movement between the two sides. The division between the two Berlins was known as the [[Berlin Wall. The United States heavily condemned the Berlin Wall and responded by placing troops on the West German side. The actions were followed by Soviet Union, which placed its troops and tanks on the East German side. That led to the iconic image of tanks facing each other at "Checkpoint Charlie," which symbolized the division of the eastern and the western parts of Germany.