On 18th Shawal/November 8, Halagu encamped on the hilltop opposite Maimundiz. The Mongol armies began to prepare for a siege. The Ismaili forces gained initial victories and rained down stones from their own mangonels upon the besiegers. The Ismaili warriors using the mangonels, were made with a pole of hard wood raised in a slanting position, supported by a strut at a point a quarter of its height from the top, and fixed in the ground at some distance from the main pole so as to support it. At the top of the pole was the emplacement for the axle to which the shaft was attached.
On the second day of fighting, the Mongols brought into a play a Chinese ballista with a range of 2,500 paces. The garrisons of Maimundiz now ceased fighting and asked for truce, which was granted. Meanwhile, on 25th Shawal/November 15, the Mongols resumed their bombardment on Maimundiz on large scale. The Ismailis strained every nerve to meet the situation and the danger hovering on their door, but they found themselves utterly helpless in the face of these nomadic hordes that poured down into the Ismaili territories like ants and locusts. At length, Ruknuddin asked for a yarligh, granting him self-conduct. He first sent down his son and another brother Iranshah with a delegation of nobles and on Sunday, the 29th Shawal, 654/November 19, 1256, he himself dismounted from the castle, embosomed with a group of dignitaries including Nasiruddin Tusi, Khwaja Asiluddin Zuzani and the vizir Muayyaduddin. He was however well received by Halagu.