“The “fourth-generation wall” (Grenzmauer 75) , known officially as “Stützwandelement UL 12.11” , was the final and most sophisticated version of the  Berlin Wall. Begun in 1975 and completed about 1980, it was constructed from 45.000 separate sections of reinforced concrete, each 3.6 metres high and 1.2 metres wide. The concrete provisions added to this version of the Wall were done so as to prevent escapees from driving their cars through the barricades (“L” shape structure). The top of the wall was lined with a smooth pipe, intended to make it more difficult to scale. This version of the Wall is the one most commonly seen in photographs, and surviving fragments of the Wall in Berlin and elsewhere around the world are generally pieces of the fourth-generation Wall.“ Wikipedia link