Kyffhäuser (kĭfˈhoizər) [key], forested mountain, c.1,550 ft (470 m), Saxony-Analt, central Germany. It is crowned by the two ruined castles of Rothenburg (7th cent.) and Kyffhausen (12th cent.) and by a huge monument to Emperor William I (erected 1896). According to legend, Emperor Frederick I (Frederick Barbarossa) sleeps bewitched in a limestone cave in the mountain, sitting at a stone table through which his beard has grown; there he awaits the time when he will go forth to restore German greatness. The legend, treated in poems by Uhland, Heine, and others, probably originally applied to Emperor Frederick II (reigned 1220–50).