The US National Security Agency (NSA) built one of its largest listening stations atop the hill, rumored to be part of the global ECHELON intelligence gathering network. “The Hill”, as it was known colloquially by the many American soldiers who worked there around the clock and who commuted there from their quarters in the American Sector, was located in the British Sector. In July 1961, Mobile Allied listening units began operations on Teufelsberg, having surveyed various other locales throughout West Berlin in a search for the best vantage point for listening to Soviet, East German, and other Warsaw Pact nations military traffic. They found that operations from atop Teufelsberg offered a marked improvement in listening ability. This discovery eventually led to a large structure being built atop the hill, which would come to be run by the NSA (National Security Agency). Construction of a permanent facility was begun in October 1963. At the request of US government, the ski lifts were removed because they allegedly disturbed the signals. The station continued to operate until the fall of East Germany and the Berlin Wall, but after that the station was closed and the equipment removed. The buildings and radar domes still remain in place.