The Berlin Wall was built in August 1961 to divide East and West Berlin. It was constructed in a single night without the knowledge of most Berliners. The wall was made of concrete and included watch towers to prevent people from crossing illegally. While some attempted to climb or run through the wall, it was very dangerous as those caught would be shot. Checkpoint Charlie provided a controlled crossing point until the East German government closed it due to spies using it. The wall stood for over 28 years until it was torn down in November 1989, reunifying the city.