The Brocken was extensively used for surveillance and espionage purposes. On the summit were two large and powerful listening stations, which could capture radio traffic in almost all of Western Europe. One belonged to Soviet military intelligence, the GRU and was also the westernmost outpost of the Soviets in Germany; the other was Department III of the Ministry for State Security in the GDR. The listening posts were codenamed "Yenisei" and "Urian". Between 1973 and 1976 a new modern television tower was built for the second channel of the GDR-TV. Today it is used by the public "Zweites Deutsches Fernsehen" (ZDF) television network. The Stasi (East German secret police) used the old tower until 1985, when they moved to a new building – now a museum. To seal the area, the entire Brocken plateau was then surrounded by a concrete wall, built from 2,318 sections, each one in weight and high. The whole area was not publicly accessible until 3 December 1989. The wall has since been dismantled, as have the Russian barracks and the domes of their listening posts. Today the old tower beside the lodge again is home to a weather station of the "Deutscher Wetterdienst".