First, there was a wall which was made up of concrete segments with a height of 4 m, usually with a concrete tube on top of it. Behind it (at the "eastern" side) there was an illuminated control area (also called death area). Refugees who had reached that area were shot without warning. A trench followed which should prevent vehicles from breaking through. Then there was a patrol track, a corridor with watchdogs, watchtowers and bunkers, and a second wall. The border cut through 192 streets, 97 of them leading to East Berlin and 95 into the GDR.