Most of the border crossings across the divide between east and west had been closed and Berlin became a place that an East German citizen could cross successfully. It was closed eventually also, first with barbed wire, then a block wall with guards, open zones, a shoot to kill order, and then a very tall concrete wall . It stayed in place for a little over 38 years, finally being opened on November 9, 1989. As they say, the rest is history.
Here is the best website I found that explains it all - http://www.berliner-mauer-gedenkstaette.de/en/mauerbau-46.html
Freedom cannot be contained by a wall, it came down eventually!
Here is a compilation of photographs from that era -
|At first it was just barbed wire|
|Then a block wall hastily erected|
|and open areas with mines|
|Shoot to kill orders came next|
|A taller wall was constructed|
|A fortified border to keep citizens in against their will but they still kept leaving|