former barrier surrounding West Berlin to keep East Germans from escaping to the West; vivid symbol of the Cold War, built in August 1961; site of U.S. President John F. Kennedy's famous “I am a Berliner” speech in 1963; original barbed wire barricade gradually replaced by a concrete wall 6 ft (2 m) high, later raised to an average height of 12 ft (4 m); eventually extended 103 mi (166 km) and included electrified fences, fortifications, and guard posts; opened by East German decree November 1989 and torn down by end of 1990, as Communism collapsed and Cold War ended