Alamut castle is located on north-west of Qazvin province and neighbor to Gazerkhan village. The castle is popular, because of Hasan Sabbah who is the promoter of Esma'ilie religion in Saljughi era. Hasan Sabbah went to Egypt Fatemian to learn the principles of Esma'ilie religion after he excluded from Malekshah Saljughy court and after a short time he was called Da'I Kabir. When he returned, he walked around Iran to find a place for his activities and finally Alamut area was chosen for this purpose. There are different ideas About the date of building, but it is belonged to early time of Islamic era. Hasan Sabbah occupied the castle on 482Hq and paid one thousand or three thousands gold dinar to excluded ruler. The castle was occupied by Holaku khan Moqol in 654Hq. the castle had lost its bullishness and changed into a prison and an exile after it was occupied and its library was fired.
The remnant monuments are very few, because of natural&unnatural disasters. Iran's cultural heritage organization, in order to get more information about the castle , dealed with scientific digging of the area.