It is located in the northeast of Gazerkhan village , which according to Hamdollah Mostowfi’s records was firstly founded in 840 A.D by Daee Ilalhagh Hasan Ebne Zeidal Bagheri then Hasan Sabbah captured it in 1090 A. D . The eastern rampart of the upper castle is constructed of stone and gypsum, and is about 10m. in length and 5m. in height. the castle is known as Alamoot or Hasan 's castle .