Rahn wrote two books linking Montségur and Cathars with the Holy Grail: "Kreuzzug gegen den Gral" ("Crusade Against the Grail") in 1933 and "Luzifers Hofgesind" ("Lucifer's Court") in 1937. After the publication of his first book, Rahn's work came to the attention of Heinrich Himmler, the head of the SS, who was fascinated by the occult and had already initiated research in the south of France. Rahn joined his staff as a junior non-commissioned officer and became a full member of the SS in 1936, achieving the rank of Obersturmführer.