Hassan-i Sabbah
The fortress probably dates back to the pre-Islamic period. Gerdkuh was situated on the Khorasan Road and guarded the routes toward the Alborz mountain range. It was refortified and transferred into the Nizari Isma'ili possession in 1100 by Ra'is Mu'ayyad al-Din Muzaffar ibn Ahmad Mustawfi (), a secret Isma'ili convert and lieutenant of the Seljuq emir Amirdad Habashi (), who in turn had acquired Gedrkuh in 1096 from Sultan Barkiyaruq. Now under Hassan-i Sabbah, Muzaffar continued as the commandant of the stronghold until being succeeded by his son Sharaf al-Din Muhammad.