Non-German Westerners could cross the border at Friedrichstraße station in East Berlin and at Checkpoint Charlie. When the Wall was erected, Berlin's complex public transit networks, the S-Bahn and U-Bahn, were divided with it. Some lines were cut in half; many stations were shut down. Three western lines traveled through brief sections of East Berlin territory, passing through eastern stations (called "," or ghost stations) without stopping. Both the eastern and western networks converged at , which became a major crossing point for those (mostly Westerners) with permission to cross.