1) The East German authorities denied they were planning it, then rubber-stamped it six weeks later: On 15 June 1961, Walter Ulbricht, the Socialist Unity Party's First Secretary and German Democratic Republic (GDR) State Council chairman, said in a press conference with international media: "Niemand hat die Absicht, eine Mauer zu errichten" (no one has the intention of erecting a wall). On Saturday, 12 August 1961, he signed the order to do just that.

2) It was often referred to as the Anti-Fascist Protection Rampart or Antifaschistischer Schutzwall by the GDR. The West Berlin city government sometimes referred to it as the "Wall of Shame", a reference to its restriction on freedom of movement.

3) There is a recognised psychological illness called "Mauerkrankheit" ? Wall Sickness , sufferers of which are afraid of confined spaces and crowds. A psychiatrist in an East Berlin mental hospital, Dr Dietfried Mueller-Hegemann, said it was an East German illness with symptoms including depression, delusions of persecution and repeated suicide attempts. One sufferer, Gitta Heinrich, is interviewed by the BBC here .

4) In between the two walls that made up the barrier was an area which became known as the Death Strip. The strip was covered with raked sand or gravel which made the footprints of defectors easy to notice and offered wall guards a clear line of fire. Beds of nails were also placed under balconies overhanging the Death Strip.

5) A total of 5,000 people successfully defected to West Berlin using a variety of methods including digging long tunnels under the wall, drifting over in a hot-air balloon or flying in ultralights, sliding along aerial wires and on one occasion, simply driving a sports car at full speed through the first, basic fortifications.