The natural geographical features of the valley surrounding Alamut largely secured the castle's defence.
Positioned atop a narrow rock base approximately 180 m above ground level, the fortress could not be taken by direct military force.
To the east, the Alamut valley is bordered by a mountainous range called Alamkuh (The Throne of Solomon) between which the Alamut River flows.
The valley's western entrance is a narrow one, shielded by cliffs over 350 m high.
Known as the Shirkuh, the gorge sits at the intersection of three rivers: the Taliqan, Shahrud and Alamut River.
For much of the year, the raging waters of the river made this entrance nearly inaccessible.
Qazvin, the closest town to the valley by land can only be reached by an underdeveloped mule track upon which an enemy's presence could easily be detected given the dust clouds arising from their passage.

The military approach of the Nizari Ismaili state was largely a defensive one, with strategically chosen sites that appeared to avoid confrontation wherever possible without the loss of life.
But the defining characteristic of the Nizari Ismaili state was that it was scattered geographically throughout Persia and Syria.
The Alamut castle therefore was only one of a nexus of strongholds throughout the regions where Ismailis could retreat to safety if necessary.
West of Alamut in the Shahrud Valley, the major fortress of Lamasar served as just one example of such a retreat.
In the context of their political uprising, the various spaces of Ismaili military presence took on the name dar al-hijra (place of refuge).
The notion of the dar al-hijra originates from the time of the Prophet Muhammad, who fled with his supporters from intense persecution to safe haven in Yathrib.
In this way, the Fatimids found their dar al-hijra in North Africa.
Likewise during the revolt against the Seljuqs, several fortresses served as spaces of refuge for the Ismailis.

In pursuit of their religious and political goals, the Ismailis adopted various military strategies popular in the Middle Ages.
One such method was that of assassination, the selective elimination of prominent rival figures.
The murders of political adversaries were usually carried out in public spaces, creating resounding intimidation for other possible enemies.
Throughout history, many groups have resorted to assassination as a means of achieving political ends.
In the Ismaili context, these assignments were performed by fidā’īs (devotees) of the Ismaili mission.
 They were unique in that civilians were never targeted.
The assassinations were against those whose elimination would most greatly reduce aggression against the Ismailis and, in particular, against those who had perpetrated massacres against the community.
A single assassination was usually employed in favour of widespread bloodshed resultant from factional combat.
The first instance of assassination in the effort to establish an Nizari Ismaili state in Persia is widely considered to be the murder of Seljuq vizier, Nizam al-Mulk.
Carried out by a man dressed as a Sufi whose identity remains unclear, the vizier's murder in a Seljuq court is distinctive of exactly the type of visibility for which missions of the fida’is have been significantly exaggerated.
 While the Seljuqs and Crusaders both employed assassination as a military means of disposing of factional enemies, during the Alamut period almost any murder of political significance in the Islamic lands was attributed to the Ismailis, whence they came to be known as the "Assassins".
The natural geographical features of the valley surrounding Alamut largely secured the castle's defence. Positioned atop a narrow rock base approximately 180 m above ground level, the fortress could not be taken by direct military force. To the east, the Alamut valley is bordered by a mountainous range called Alamkuh (The Throne of Solomon) between which the Alamut River flows. The valley's western entrance is a narrow one, shielded by cliffs over 350 m high. Known as the Shirkuh, the gorge sits at the intersection of three rivers: the Taliqan, Shahrud and Alamut River. For much of the year, the raging waters of the river made this entrance nearly inaccessible. Qazvin, the closest town to the valley by land can only be reached by an underdeveloped mule track upon which an enemy's presence could easily be detected given the dust clouds arising from their passage.
The military approach of the Nizari Ismaili state was largely a defensive one, with strategically chosen sites that appeared to avoid confrontation wherever possible without the loss of life. But the defining characteristic of the Nizari Ismaili state was that it was scattered geographically throughout Persia and Syria. The Alamut castle therefore was only one of a nexus of strongholds throughout the regions where Ismailis could retreat to safety if necessary. West of Alamut in the Shahrud Valley, the major fortress of Lamasar served as just one example of such a retreat. In the context of their political uprising, the various spaces of Ismaili military presence took on the name dar al-hijra (place of refuge). The notion of the dar al-hijra originates from the time of the Prophet Muhammad, who fled with his supporters from intense persecution to safe haven in Yathrib. In this way, the Fatimids found their dar al-hijra in North Africa. Likewise during the revolt against the Seljuqs, several fortresses served as spaces of refuge for the Ismailis.
In pursuit of their religious and political goals, the Ismailis adopted various military strategies popular in the Middle Ages. One such method was that of assassination, the selective elimination of prominent rival figures. The murders of political adversaries were usually carried out in public spaces, creating resounding intimidation for other possible enemies. Throughout history, many groups have resorted to assassination as a means of achieving political ends. In the Ismaili context, these assignments were performed by fidā’īs (devotees) of the Ismaili mission.  They were unique in that civilians were never targeted. The assassinations were against those whose elimination would most greatly reduce aggression against the Ismailis and, in particular, against those who had perpetrated massacres against the community. A single assassination was usually employed in favour of widespread bloodshed resultant from factional combat. The first instance of assassination in the effort to establish an Nizari Ismaili state in Persia is widely considered to be the murder of Seljuq vizier, Nizam al-Mulk. Carried out by a man dressed as a Sufi whose identity remains unclear, the vizier's murder in a Seljuq court is distinctive of exactly the type of visibility for which missions of the fida’is have been significantly exaggerated.  While the Seljuqs and Crusaders both employed assassination as a military means of disposing of factional enemies, during the Alamut period almost any murder of political significance in the Islamic lands was attributed to the Ismailis, whence they came to be known as the "Assassins".
Alamut Castle