“Berlin Wall, German Berliner Mauer, barrier that surrounded West Berlin and prevented access to it from East Berlin and adjacent areas of East Germany during the period from 1961 to 1989. In the years between 1949 and 1961, about 2.5 million East Germans had fled from East to West Germany, including steadily rising numbers of skilled workers, professionals, and intellectuals.”

via Berlin Wall (wall, Berlin, Germany) — Encyclopedia Britannica.