Alamut was a mountain fortress located in Alamut region in the South Caspian province of Daylam near the Rudbar region in 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 Nizari Ismai'lis of Persia , along with a smaller subgroup known as the Assassins in Syria , functioning as the headquarters of their state , which was in fact a series of unconnected strategic strongholds scattered throughout Persia (Iran) and Syria , surrounded by huge swathes of hostile territory (the Seljuq Empire) . In 1256 , Rukn-ul-Din Khurshah 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 .