By 1961 – ten years after its foundation – GDR had lost to the West 3.5 million East Germans, or approximately 20% of its population, and its leaders acknowledged that the flight of its young, well-educated citizens was so serious it threatened the regime's existence.
In June of the year, GDR's top Communist, Walter Ulbricht, still denied that "anyone considered building a wall" to close the escape route to West Germany. But two months later, after he received an O.K. from Soviet premier Nikita Khrushchev, Ulbricht ordered – typically, in a cabinet meeting disguised as a Saturday night garden party – the construction of the Berlin Wall.
At midnight on August 12, East German police and army closed the border and by Sunday morning, East German troops and workers had begun to tear up streets and install barbed-wire entanglements and fences. Brazen as it was, the subsequent construction of the parallel concrete walls was carefully located inside East Berlin to ensure that the complex did not encroach on the Allied sectors.

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