The Berlin Wall was a guarded concrete barrier that divided Berlin from 1961 to 1989. It encircled West Berlin, separating it from East German territory. Construction of the wall was commenced by the German Democratic Republic (GDR, East Germany) on 13 August 1961. The Wall cut off West Berlin from surrounding East Germany, including East Berlin. It included guard towers placed along large concrete walls and a wide area containing anti-vehicle trenches, beds of nails, and other defenses.

Source: Wikipedia