Alamut was a mountain fortress located in Alamut region in the South Caspian province of Daylam near the Rudbar region in Persia (Iran), approximately 100 km from present-day Tehran.

Between 1090 and 1256 AD, under the leadership of Hasan-i Sabbah, Alamut became the site of intense activity for the Shi’a Nizari Ismai’lis, functioning as the headquarters of their state, which was consisted a series of unconnected strategic strongholds scattered throughout Persia and Syria, surrounded by huge swathes of hostile territory (the Seljuq Empire). In 1256, Ruknu-d-Dīn Khurshāh surrendered the fortress to the invading Mongols, and its famous library holdings were destroyed. Sources on the history and thought of the Ismailis in this period are therefore lacking and the majority extent is written by their detractors. After the Mongol destruction, the castle was of only regional significance, passing through the hands of various local powers. Today, it lies in ruins, but because of its historical significance, it is being developed by the Iranian government as a tourist destination.

The origins of the Alamut fortress can be traced back to the Justanid ruler, Vahsudan, who, during a hunting trip, witnessed a soaring eagle perch down high on a rock. Realizing the tactical advantage of the location, he chose the site for the construction of a fortress, which was called “Aluh āmū[kh]t” likely meaning “Eagle’s Teaching” or “Nest of Punishment”. Alamut remained under Justanid control until the arrival of the Ismaili chief data (missionary) Hasan-i Sabbah to the castle in 1090 AD, marking the start of the Alamut period in Ismaili history.