Some Berlin Wall trivia:
* The wall was not between East and West Berlin, but between West Berlin and the GDR, entirely enclosing West Berlin, naturally. (45 km bordered East Berlin, 113 km Potsdam, the state around Berlin.)
* Just two months before the wall was built, at a press conference, Walter Ulbricht, then head of the GDR, said that nobody had the intention of building a wall. "Niemand hat die Absicht, eine Mauer zu errichten."
* It wasn't just a wall, but an entire corridor 50m to several hundred metres wide (on the "Eastern" side), consisting of a smaller wall ("Hinterlandmauer"), sometimes corridors for K-9s (German shepherds, naturally), anti-tank obstacles ("Czech hedgehog"), observation towers (302 by the time the wall came down), control strips "Kontrollstreifen" of freshly harrowed sand so trespassers would leave tracks, then "the wall", then a few more metres GDR, then the actual legal border. (However, no "Selbstschussanlagen SM-70", shotguns rigged to fire automatically - those were only deployed at the border to West Germany.)
* There were 2300 border troops deployed at any time, mostly in pairs to control each other, but rotating, so that they couldn't form a bond. They were under an order to shoot trespassers, the infamous "Schiessbefehl".
* Some 100 to 200+ people died trying to cross the wall. It is surprisingly hard to put an exact number on it.
* There were some "enclaves" (exclaves?) like the Lenné-Dreieck (Lenné-triangle): on the "western" side of the wall, but officially belonging to the East, so effectively a no-man's land.
* One of the iconic events precipitating the fall was in Sept 1989. Many (thousands) of East Germans had traveled to Prague, Czechoslovakia (not part of the USSR, but of the Eastern Bloc), and climbed over the fence of the West German embassy there, camping on the grounds. On 30 Sept, the foreign minister of West Germany (after long negotiations with USSR foreign minister Shevardnadse), Hans-Dietrich Genscher, appeared on the balcony to tell those refugees that they could go on to West Germany. The rest of the speech was basically drowned out by cheering as soon as the crowd heard "Ausreise". See here from about 1:20. https://www.youtube.com/watch?v=Ov9IHjX8UF4
* Then, on 9 Nov 1989, the wall fell, and it was a surprisingly silly culmination of the revolution. The East German authorities knew that they couldn't carry on, and were planning to gradually open the borders from December onwards (given that people could flee via Czechoslovakia anyway). They started working on legislation, and there was lots of discussions going back and forth (would people that left be allowed to return, etc.) On Nov 9, they sent the first secretary of the party (Sozialistische Einheitspartei Deutschlands) in East Berlin, Günter Schabowski, on a press conference to talk about these plans, but he hadn't attended the deliberations and was basically reading from some notes he had been handed. An Italian reporter asked about it the border, and Schabowski announced these plans for liberalisation, live on TV. He was then asked when these would go into effect, and he shuffled around in those papers and said "as far as I know, that's applicable now, immediately". People stormed the border ("first gradually, then suddenly"), and the rest was history. See around 0:40 here: https://www.youtube.com/watch?v=Mn4VDwaV-oo