Bābak Fort, Babak Castle, or Bazz Galasi (Persian: دژ بابک or قلعه بابک), also known as the Immortal Castle or Republic Castle, is a large citadel on the top of a mountain in the Arasbaran forests, which is located 16 km southwest of Kalibar City in northwestern Iran.
It has been identified as the stronghold of Bābak Khorramdin, the leader of the Khurramites in Azerbaijan who fought the Abbassids.