East Berlin was the name given to the eastern part of Berlin between 1949 and 1990 when it was part of the German Democratic Republic. From 13 August 1961 until 9 November 1989 East Berlin was separated from West Berlin by the Berlin Wall.
In 1974, Roberta Lincoln and Gary Seven conducted an operation in the Soviet embassy, which was located in East Berlin. Afterward the pair was forced to run from East German border guards stationed at the Berlin Wall. (TOS novel: The Rise and Fall of Khan Noonien Singh, Volume 1)