Alamut (Persian: الموت‎‎, meaning "eagle's nest") 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 (60 mi) 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 NizariIsmai'lis, functioning as the headquarters of their state, which consisted of 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 extant are 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.