"In about 488/1095, the Ismailis of Alamut took possession of one of the most important strongholds, Girdkuh, the old Diz Gunbadan (the domed fort) in Qumis. The valiant garrison of Girdkuh however continued to resist its Mongol besiegers for 13 years after the reduction of Alamut. In the biography of Kuo K'an, the Chinese officer in Mongol forces, it is recorded that Girdkuh was situated on the top of the mountain Tan-han (i.e., Damghan), and was only accessible by ladders, which were guarded by the most valiant troop, vide Mediaeval Researches from Eastern Asiatic Sources (London, 1888, 1:122) by E. Bretschneider. In another Chinese source, Hsi Shin Chi, we find a record of the journey of a Chinese envoy, Chang Te, sent by Halagu in 1259; wherein it is described Girdkuh as a mountain fortress "on a very steep rock, which could not be reached by arrows or stones. The rock was so steep that when one looked up, his cap fell off." Haython however writes in Flos Historianrum Terrae Orientis that, "Tigado (Girdkuh) was an impregnable castle, well furnished with all necessaries, and was so strong that it had no fear of attack on any side." At length, the garrison came down not due to starvation, but it was the lack of adequate clothing against the severe winter cold that ultimately broke their spirits. The final surrender reported to have taken place on 29th Rabi II, 669/December 15, 1270.