started the explosion). In 1803, Königstein passed to the Principality of Nassau-Usingen, which itself later merged with Nassau-Weilburg to form the Duchy of Nassau. By 1866 it was in Prussian hands, and since 1945, it has been part of Hesse. The three constituent communities mentioned herein were amalgamated with Königstein as part of Hesse's municipal reforms in 1972. Königstein enjoyed an economic upswing from less wealthy times when the coldwater spa first opened in 1851. It reached its high point just before the First World War broke out. The designation was granted in 1935, and is still borne by the town, and now also independently by the constituent community of Falkenstein. Jewish health resort and summer residence of the Frankfurt Jews Königstein was regarded as a "Jewish spa" – this was especially in the era of National Socialism a topic. The city became famous as "Jewish spa" mainly due to the high proportions of Jewish guests (for example Otto Klemperer, Kurt Hahn, Carl Sternheim, Botho Graef, Reinhold Lepsius), who stayed in the internationally famous sanitarium Dr. Kohnstamm (the name stuck even after the death of the founder Oskar Kohnstamm in 1917) and Hotel Cahn, which offered kosher food. For these reasons, Königstein was an attractive city to visit for a day trip for many Jews in Frankfurt. Königstein became even more easily accessible from Frankfurt am Main in 1902, when the railway between Königstein and Frankfurt was built. Königstein was also the residence of prominent Jewish citizens (for example Mathilde Hannah von Rothschild, Sigmund Kohn-Speyer, L. Albert Hahn, Hermann Wronker, Albert Katzenellenbogen, Julius Blau, Max Neisser, Adolf Sabor, Selmar Spier, the family of Richard Musgrave), who in turn brought their friends and guests there. The poet Stefan George, e.g., initially often visited his school friend Oskar Kohnstamm, and then after Kohnstamm's death in 1917 and the sale of Kohnstamm's sanatorium, moved to Königstein to be near his sister, Anna George. In her apartment he received members of the George circle for which special rooms had been rented. These include for example the poet Ernst Morwitz, with whom he went for long walks. George's and Kohnstamm's honored school friend Karl Wolfskehl had contacts to the Sanatorium Dr. Amelung, whose director had been a friend of Oskar Kohnstamm. After Kohnstamm's death in 1917 until 1938 the owner of the renowned Kohnstamm sanatorium was Carl Frankl (also Jewish). Carl was a brother of