 The walled-up Altstadt quarter became the nucleus of the larger Spandau Fortress, built under Prussian rule after the Napoleonic Wars in the early 19th century, also a centre of the German arms industry.Today the Altstadt quarter is served by Rathaus Spandau and Altstadt Spandau stations on the Berlin U-Bahn line .Berlin-Spandau station, served by S-Bahn, regional and intercity railway routes, is situated to the south of the Altstadt.