well into the 19th century – a place of high-level prostitution. Traces of this hidden agenda of the city's history are found in the 18th-century guidebooks to Aachen as well as to the other spas. The main indication for visiting patients, ironically, was syphilis; only by the end of the 19th century had rheumatism become the most important object of cures at Aachen and Burtscheid. Aachen was chosen as the site of several important congresses and peace treaties: the first congress of Aachen (often referred to as the Congress of Aix-la-Chapelle in English) on 2 May 1668, leading to the First Treaty of Aachen in the same year which ended the War of Devolution. The second congress ended with the second treaty in 1748, ending the War of the Austrian Succession. In 1789, there was a constitutional crisis in the Aachen government, and in 1794 Aachen lost its status as a free imperial city. 19th century On 9 February 1801, the Peace of Lunéville removed the ownership of Aachen and the entire "left bank" of the Rhine from Germany (the Holy Roman Empire) and granted it to France. In 1815, control of the town was passed to the Kingdom of Prussia through an agreement reached by the Congress of Vienna. The third congress took place in 1818, to decide the fate of occupied Napoleonic France. By the middle of the 19th century, industrialisation had swept away most of the city's medieval rules of production and commerce, although the entirely corrupt remains of the city's medieval constitution were kept in place (compare the famous remarks of Georg Forster in his Ansichten vom Niederrhein) until 1801, when Aachen became the "chef-lieu du département de la Roer" in Napoleon's First French Empire. In 1815, after the Napoleonic Wars, the Kingdom of Prussia took over within the new German Confederation. The city was one of its most socially and politically backward centres until the end of the 19th century. Administered within the Rhine Province, by 1880 the population was 80,000. Starting in 1838, the railway from Cologne to Belgium passed through Aachen. The city suffered extreme overcrowding and deplorable sanitary conditions until 1875, when the medieval fortifications were finally abandoned as a limit to building and new, better housing was built in the east of the city, where sanitary drainage was easiest. In December 1880, the Aachen tramway network was opened, and in 1895