This free access, especially after the closure of the Inner German border, allowed the Eastern Bloc emigration and defection to occur.
Border officials and customs agents would monitor incoming and outgoing traffic according to established procedures, at times with the utmost scrutiny.
The actual inspections of vehicle and pedestrian traffic were carried out by the passport control units (German abbreviation PKE, short for Passkontrolleinheiten).
The passports, identification cards, etc., could be transmitted from the inspection sites to a processing center using closed-circuit television and ultraviolet light, where they were recorded.
From there, commands were issued using a numeric display to the passport control unit, for example "flip page", "request additional documentation", "delay processing", ask predefined questions, etc.
Visas for day trips restricted to East Berlin were issued without previous application in a simplified procedure at the border crossing.
In 1963, negotiations between East and West resulted in a limited possibility for visits during the Christmas season that year (Passierscheinregelung).
This regulation remained in force essentially until the fall of the wall, but over the years several exceptions to these rules were introduced, the most significant being: However, each visit had to be applied for individually and approval was never guaranteed.
The opening of the Brandenburg Gate was merely a public relations formality which took place on 22 December 1989 at the request of then-Chancellor Helmut Kohl.
Thus, in the weeks between 9 November 1989 and 23 December 1989, East Germans could travel more freely than Westerners as they were able to cross into West Berlin with just passport checks.
International travel is now routed via Schönefeld airport which is situated south of the city in Brandenburg and all Cold War-specific border control procedures have disappeared altogether.
Modern day checkpoints are staffed by German Federal Police and Customs for normal international traffic screening purposes.