south of the Landwehrkanal, which lasted from 17 June 1875 until 15 October 1882. A railway line once ran through Potsdamer Platz: a connecting line opened in October 1851 and running around the city just inside the customs wall, crossing numerous streets and squares at street level, and whose purpose was to allow goods to be transported between the various Berlin stations, thus creating a hated traffic obstruction that lasted for twenty years. Half a dozen or more times a day, Potsdamer Platz ground to a halt while a train of 60 to 100 wagons trundled through at walking pace preceded by a railway official ringing a bell. The construction of the Ringbahn around the city's perimeter, linked to all the major stations, allowed the connecting line to be scrapped in 1871, although the Ringbahn itself was not complete and open for all traffic until 15 November 1877. Potsdamer Platz was served by both of Berlin's two local rail systems. The U-Bahn arrived first, from the south; begun on 10 September 1896, it opened on 18 February 1902, with a new and better sited station being provided on 29 September 1907, and the line itself being extended north and east on 1 October 1908. In 1939 the S-Bahn followed, its North-South Link between Unter den Linden and Yorckstraße opening in stages during the year, the Potsdamer Platz S-Bahn station itself opening on 15 April. By the second half of the 19th century, Berlin had been growing at a tremendous rate for some time, but its growth accelerated even faster after the city became the capital of the new German Empire on 18 January 1871. Potsdamer Platz and neighbouring Leipziger Platz came into their own afterward. Now firmly in the centre of a metropolis whose population eventually reached 4.4 million, making it the third largest city in the world after London and New York, the area was ready to take on its most celebrated role. Vast hotels and department stores, hundreds of smaller shops, theatres, dance-halls, cafés, restaurants, bars, beer palaces, wine-houses and clubs, all started to appear. Some of these places became internationally known. Also, a very large government presence, with many German imperial departments, Prussian state authorities and their various sub-departments, came into the area, taking over 26 former palaces and aristocratic mansions in Leipziger Platz, Leipziger Strasse and Wilhelmstraße. Even the Reichstag itself, the German Parliament, occupied the