The Berlin Wall went up in the early hours of August 13, 1961, and was constantly modified and reinforced until it fell 28 years later, having cost the lives of at least 136 people who tried to cross it.
The total length was 155 kilometres (96 miles), of which 43 kilometres ran roughly north-south, cleaving Berlin in two, while another 112 kilometres isolated the enclave of West Berlin from the surrounding East German state.
A "no-man's land" ran the length of the Wall, varying from the width of a street to about 300 metres (328 yards), effectively blighting the immediate terrain around for normal human use.
For more than 106 kilometres of its length, the Wall was composed of panels of reinforced concrete to a height of 3.60 metres, with a rounded top providing no toe- or hand-hold for any would-be climber. The rest was composed of metallic grill fencing.
A total of 302 watchtowers and 20 bunkers were manned by seven units of 1,000 to 1,200 soldiers each. The Wall was also protected by 124 kilometres of patrol routes, 127 detector and alarm devices, 259 paths for guard dogs and 105 kilometres of ditches dug to trap vehicles in.
The watchtowers, some 250-300 metres apart in the city centre, were connected by paths for the guards on patrol. With lampposts every 30 metres, the Wall was also the best-illuminated part of all Berlin. By contrast, East Berlin was quite dark at night.
The land adjoining the Wall was under constant examination to detect any footprints, but devices which automatically fired shots at those who ventured onto the concrete structure were dismantled in later years. Instead, a second, inner wall was built along it on the eastern side.
Nevertheless, at least 5,000 people managed to get across.
Demolition began rapidly after the East German authorities gave the order to allow people free passage through the Bernauerstrasse crossing point on the evening of November 9, 1989. Souvenir hunters carried away huge sections but some of it has been preserved in place.
In parallel with the Berlin Wall, the 1,400-kilometre-long inter-German border was also marked by barbed wire, metal grill fences equipped with electronic detection equipment, and landmines.