Ismaili History 639 - Beginning of the Mongol operations
Soon afterwards, Guyuk dispatched Eligidei to Iran at the head of reinforcements for the Mongol armies already stationing there, with instructions to assume supreme command in reducing the Muslim holds, beginning with Alamut. Guyuk intended to follow after, but his death prevented the operations, which was charged some six years later, to his nephew and successor Mongke (1251-1259), who appointed his brother Halagu (1256-1265) to command an army to Iran, Iraq and Egypt according to the resolution of the Mongol National Assembly (quriltai) held in 649/1251. Halagu did not reach Iran before the beginning of 654/1256, but had dispatched an advance army of 12,000 men from Mongolia in 650/1252 in command of Ket-Buqa to join with the Mongol garrison already camping in Iran. Ket-Buqa crossed the Oxus in 651/1253 and soon afterwards, attacked the Ismaili strongholds in Kohistan. His troops drove off the cattle of the people of Tun, Turshiz and Zir-kuh and slaughtered and pillaged throughout that region. The towns of Tun and Turshiz were however captured, but the Ismailis recovered Tun very soon. Ket-Buqa also reached at the foot of Girdkuh with 5,000 men, where he constructed elaborate siegeworks, digging a trench around the castle, and erecting a wall around the trench. The men then formed a ring behind that wall, and a second wall and a trench were constructed around the men, so that they were apparently left secure in the middle with no possibility of attack from either side.
Leaving his officer, Buri with the charge of siege at Girdkuh, Ket-Buqa proceeded to attack the castle of Mihrin, near Girdkuh and Shahdiz. In Shawal, 651/December, 1253, the Ismaili garrison of Girdkuh made a valiant nocturnal assault on the Mongols, killing a hundred of them, including Buri. The siege however continued and in the interim, the disease of cholera broke out in the summer of 652/1254. It was reported to Alamut that most of the garrisons were perishing and the castle was on the verge of falling. Alauddin Muhammad immediately supplied reinforcements, including his three officers at the head of 110 men, each carrying a load of two maunds of henna (Latin Lawsonia inermis, Arabic hinna, the shrub) and three maunds of salt. The garrison's stock of salt had been exhausted, and as for the henna, we are told by the author of 'Jamiut Tawarikh', himself a physician, that there had not been prescribed in the books of medicine that henna was a drug against cholera. The people of Girdkuh had an experience however that once water being scarce, some of them had drunk that henna water and were cured. It was for this reason that they had asked for henna from Alamut. The 110 men forced their way through the ranks of the besiegers, suffering only a single causalty; one of them fell into the trench and dislocated his leg; his comrades lifted him on to their shoulders and carried him into the castle. The garrison, thus restored to its full strength, and continued its resistance until 659/1270.
Halagu was yet in Samarkand and was about to cross Oxus on the eve of the death of Alauddin Muhammad, who, according to Peter Brent, might have been strong enough to resist for a long time against the Mongols, vide 'The Mongol Empire' (London, 1976, p. 135)