(1756–1763), the basement rooms were probably used as a military prison. Prussian state ownership During the 18th and 19th centuries, the castle fell progressively into ruin. In 1802, during German mediatisation the castle came into the possession of the Prussian state. On 11 January 1815, the North Tower was gutted by a fire that was started by a lightning strike; only the outer walls remained. From 1832 to 1934, a rectory existed in the eastern part of the south wing of the castle. District of Büren ownership In 1924, the castle became the property of the district of Büren and was changed into a cultural center. By 1925, the castle had been renovated into a local museum, banquet hall, restaurant and youth hostel. At the end of the Twenties, the North Tower again proved to be the weak point of the architecture, and had to be supported by guy wires in winter 1932/33; the preservation of the castle was supported by the "Club for the preservation of the Wewelsburg" (Verein zur Erhaltung der Wewelsburg). After 1925, the renovation activities decreased. Nazi era In 1932, the local head of the district authority (Landrat) ordered about seventy members of the Freiwilliger Arbeitsdienst (FAD), (voluntary labour service), to be housed at the Wewelsburg. They were unemployed and supported by the state as Notstandsarbeiter (literally: "crisis workers"). Through the rent, the district of Büren thus hoped to recoup some of the running costs of the castle. However, in early 1933, negotiations to set up a full-sized camp for 214 FAD participants failed. Prior to the Nazi party taking power, Heinrich Himmler, as leader of the SS, had decided that the organization should have a retreat at a castle "in the heartland of Hermann der Cherusker" (Armin the Cheruscian). Initially Himmler showed an interest in but negotiations failed in early 1933; he then visited Wewelsburg, at the suggestion of a local Nazi leader, . Himmler decided to buy or lease the castle on his first visit on 3 November 1933. His architect, Hermann Bartels was able to draw on existing plans for the FAD camp, for the now envisaged Reichsführerschule SS (SS Leadership School). This school was mainly intended to ensure a unified ideological training of the SS leadership and would be run by the Rasseamt of the SS. Negotiations were difficult, however, since the Landrat of Büren was unwilling to give up control of