open again. Industrial revolution, Imperial Germany and the Weimar Republic In 1837, steamship travel began on the upper Elbe. A few years later, in 1848, a railway line connecting Dresden and Pirna opened. In 1880, the first section of the Sekundärbahn-type railway line from Pirna to Gottleuba, the Gottleuba Valley railway was opened. The line was closed in 1976. In 1894, another railway line opened was the Pirna–Großcotta railway, connecting Pirna with the Lohmgrund, a major location of Saxonian sandstone quarries. It closed in 1999. Pirna became an industrial town in 1862 with the building of factories. Mechanical engineering, glass, cellulose and rayon production also expanded. In 1875, the sandstone Elbbrücke was completed. During the First World War Pirna became a garrison and the engineer battalions 12 and 5 of the Royal Saxon field artillery regiment No. 64 were billeted on Rottwerndorfer Straße. In 1922/23, the town incorporated several municipalities including Posta, Niedervogelgesang, Obervogelgesang, Copitz, Hinterjessen, Neundorf, Zuschendorf, Rottwerndorf and Zehista. The population totaled about 30,000 inhabitants. National Socialism and Second World War From early 1940 until end of June 1942, a part of the large mental asylum within Sonnenstein Castle was converted into a euthanasia killing center: the Sonnenstein Nazi Death Institute. It was a testing ground for initial development of certain methods, later generally adopted and refined for usage associated with the Final Solution. A gas chamber and crematorium were installed in the cellar of the former men's sanitary (building C 16). A high brick-wall on two sides of the complex shielded it from outside view. Four buildings were located inside this brick-wall shielding. They were used as offices, living rooms for the personnel, etc. Sleeping quarters for the men responsible for incinerating the bodies were provided in the attic of building C 16. It is possible that other sections of the buildings were also used by Action T4. From end of June 1940 until September 1942, approximately 15,000 persons were killed in the scope of the mass murder by involuntary euthanasia program and the Sonderbehandlung Action 14f13. The personnel list consisted of about 100 persons. One third of them were reassigned to the extermination camps in occupied Poland, because of their recent experiences in deception, killing, gassing and incinerating of people. There, they were trained by the detachments responsible for organized killing in camps like Treblinka. These killings ceased after pressure was exerted on the authorities by