Between the platforms "B" and "C" was a metal-glass barrier that practically fulfilled the same function as the Berlin Wall: East German border troops separated the station into two completely isolated areas, both fully under armed control, one for people within East Berlin and the other for transit travellers, persons switching between the different westbound train lines, and the few Easterners with a hard-to-obtain exit visa, all within one station building with a maze of connecting hallways, barriers, numerous cameras, armed guards with sniffer dogs, plain-clothes agents, and a loggia under the roof for surveillance by armed border patrol and Stasi officers.