Lines S3, S5, S7, S9, and S75 are east-west lines using the "Stadtbahn" cross-city railway. The western termini are located at Potsdam and Spandau, although the S5 only runs as far as Westkreuz and the S75 to Ostkreuz. The eastern termini are Erkner, Strausberg Nord, Ahrensfelde, and Wartenberg. The S9 uses a connector curve ("Südkurve") at Ostkreuz to switch from the "Stadtbahn" to the South-eastern leg of the "Ringbahn". Another curve, the "Nordkurve" to the North-eastern "Ringbahn", was originally served by the S86 line, but it was demolished in preparation of the rebuilding of "Ostkreuz" station and was not rebuilt afterwards. Both connector curves were heavily used in the time of the Berlin Wall, as trains coming from the North-Eastern routes couldn't use the West Berlin North-South route and the Southern leg of the pre- and post-Wall "Ringbahn" was in West Berlin.