The natural geographical features of the valley surrounding Alamut largely secured the castle's defence. Positioned atop a narrow rock base approximately 180 meters 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 350m 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. During the mid-12th century the Assassins captured or acquired several fortresses in the Nusayriyah Mountain Range in coastal Syria, including Masyaf, Rusafa, al-Kahf, al-Qadmus, Khawabi, Sarmin, Quliya, Ulayqa, Maniqa, Abu Qubays and Jabal al-Summaq. For the most part, the Assassins maintained full control over these fortresses until 1270–73 when the Mamluk sultan Baibars annexed them.