The Helmstedt–Marienborn border crossing (), named Grenzübergangsstelle Marienborn (GÜSt) (border crossing Marienborn) by the German Democratic Republic (GDR), was the largest and most important border crossing on the Inner German border during the division of Germany. Due to its geographical location, allowing for the shortest land route between West Germany and West Berlin, most transit traffic to and from West Berlin used the Helmstedt-Marienborn crossing. Most travel routes from West Germany to East Germany and Poland also used this crossing. The border crossing existed from 1945 to 1990 and was situated near the East German village of Marienborn at the edge of the Lappwald. The crossing interrupted the Bundesautobahn 2 (A 2) between the junctions Helmstedt-Ost and Ostingersleben. History First checkpoints A checkpoint was established on the site on 1 July 1945, which was on the demarcation line between the British and Soviet occupation zones. Its scope included the interzonal railway traffic as well as the motor vehicle traffic on the Reichsautobahn between Hanover and Berlin. The checkpoint buildings were located directly on the zones' border, and consisted of little more than temporary wooden buildings. The most important inner-German checkpoint, the Autobahn crossing at Helmstedt was named Alpha by the Western Allies. Its counterpart in the Berlin southern borough of Dreilinden was named Bravo. The connection between these checkpoints gained its importance from being the shortest connection between the western zones and Berlin, at . During the Berlin Blockade, which endured from June 1948 to May 1949, the Soviet checkpoint was closed. The border was initially manned by the Royal Military Police and the Group of Soviet Occupation Forces In Germany. From 1950 onwards, the East German (later the ) performed the border control on the eastern side of the checkpoint while the Soviet Army escorted NATO military traffic to and from West Berlin. Due to the increasing tensions between the Western Allies and the Soviet Union during the Cold War, the border crossing was expanded extensively and security was increased during the following years. However, the original checkpoint was eventually regarded too unsafe to operate efficiently. Expansion in the 1970s Between 1972 and 1974, the GDR erected a new control portal on a field situated on a hill near Marienborn, about east of the border. The control portal was staffed with as many as 1,000 passport control, customs, and border police employees. The buildings were linked with a tunnel