From their rallying point in the Seven River Region the armies of Chingis Khan descended upon the city of Otrār. As noted, Nasawi wrote that the Khwarezmshah sent 20,000 horsemen to defend the city. Juvaini on the other hand claimed that the Khwarezmshah sent a commander named Qaracha Khass-Hajib to Otrār with 10,000 men and had also sent 50,000 troops from his auxiliary armies. In any case. it appeared at first glance that the city was well-defended. The Gāyer Khan had strengthened and reenforced the walls of the the Rabad (outer city, the Shahristan (walled inner city), and the Ark, or citadel, and had laid in a vast store of weapons. Despite all this when he climbed the city wall to view the arrival of the Mongol army, he “bit the back of his hand in amazement” at the “tossing sea of countless hosts and splendid troops” arrayed before him, according to Juvaini. The entire multitude may have numbered 150,000 men.
The siege of Otrār probably begin in September of 1219. Chingis realized early on that his entire army was not needed to take Otrār, and he may have not wanted to give the other cities of Transoxiania more time to prepare their defenses. After the city was surrounded and no escape possible for its defenders he decided to split up his army. Several tümen, including a tümen of Uighur auxiliaries (a division numbering 10,000 each) of troops), under the command of his two middle sons Chagatai and Ögedei were ordered to stay and continue the siege of Otrār. His oldest son Jochi and several tümen were dispatched down the Syr Darya toward Jand and other cities. Half a tümen proceeded up the valley of the Syr Darya to Khojend and Fanakat. Chingis himself and his youngest and perhaps favorite son Tolui would lead the main body of the army to Bukhara, the city which rivaled Samarkand as the most important in Transoxiana.
There were soon signs of rifts among the city’s leadership. After the Khwarezmshah had seized control of Otrār in 1210 city or early 2011 he had executed the father, uncle, and various other relatives of a prominent local official named named Badr al-Din al-Amid. Despite the transgressions of his family members Badr al-Din al-Amid had remained on as the civil governor of the city. He nursed a grudge against the Khwarezmshah, however, and he was only too eager to avenge the murder of his relatives by siding with the Mongols who now appeared at the city’s walls. He may have also realized he was buying his way out of a doomed city. Intimately familiar with the political situation in Transoxiania, he was able to give Chingis detailed intelligence about the fault lines in the Sultan’s court, including dirt about the feud between the Sultan and his mother and the military party she headed. Chingis would later put this information to good use. Also, it will be remembered that one of the proposals given by the Khwarezmshah’s military council had been to allow Chingis into Transoxiana and then use the defenders’ supposedly superior knowledge of the the local countryside to corner and ambush his troops. This advantage quickly evaporated as Chingis received intimate knowledge about the roads and conditions in the countryside from Badr al-Din al-Amid and other Muslim collaborators. As Barthold points out, “The strategic plans of Chingiz-Khan and their brilliant execution prove that the geographical conditions were well known to him.”
For four months the battle raged before the walls of Otrār. As it become increasingly obvious the city would never escape from the noose the Mongols had thrown around it the military commander Qaracha Khass-Hajib advised surrender. Gāyer Khan refused, knowing full well that given his role in The Plundering Of The Mongol Trading Caravan and the execution of Chingis’s emissary he could expect no quarter from the Mongols. To surrender was to die. Instead he argued: “‘If we are unfaithful to our master [the Sultan], how shall we excuse our treachery, and under what pretext shall we escape from the reproaches of Moslems?”
Juvaini’s account of what happened next is muddled. Apparently one night Qaracha Khass-Hajib opened the Sufi-Khana Gate to the city and sent some of his forces outside the walls to do battle with the Mongols. That night the Mongols somehow entered by the same gate and managed to take Qaracha Khass-Hajib prisoner. Apparently now that he was in the hands of the Mongols he and some of his officers attempted to switch allegiance and throw in their lot with the besiegers. Unfortunately for Qaracha Khass-Hajib, the Mongols took a dim view of such expedient, self-serving behavior on the battlefield. “Thou has been unfaithful to your own master in spite of his claims on thee on account of past favors. Therefore neither can we expect fidelity of thee.” Qaracha Khass-Hajib and his companions were then introduced to the Destroyer of Delights. There is no mention by Juvaini if they were tortured before their executions or how they died. He says only that he and his companions managed to “attain to a degree of martyrdom.”
Both the outer and inner sections of the city were overrun by the Mongols. The entire populace was herded outside the walls ”like a flock of sheep” and the now-empty city looted by the victorious Mongols and their auxiliaries. If Gāyer Khan had harbored any remaining doubts about fighting on against the Mongols the fate of Qaracha Khass-Hajib must have squelched them. He and 20,000 of his men retreated behind the walls of the Ark (citadel) and prepared to fight “as long as one of them had breath in his body.” They did not go down easily. “They set their hearts upon death and having bid themselves farewell sallied forth fifty at a time and spitted their bodies upon spears and swords.” They got their wish for martyrdom but not before inflicting serious damage. Even Juvaini admits that “many from the Mongol army were slain.”
After a month of vicious fighting only Gāyer Khan, two of his bodyguards, and members of his harem remained alive. They took final refuge on the roof of the Citadel. The Mongols had strict order to take Gāyer Khan alive. They killed his bodyguards and Gāyer Khan finally shot the last of his arrows. His women then handed him bricks which he hurled down on his tormenters. Finally even these were exhausted. In light of his eventual fate he would have been well advised to commit suicide by jumping off the top of the Citadel. Instead, he allowed himself to be captured and bound in heavy chains. Eventually he was taken to Samarkand for his inevitable meeting with the Destroyer of Delights, the details of which will be related later. The Citadel was demolished and the walls of the city completely razed. Many of the common people of the city were rounded up and made to serve as levies in upcoming battles. Artisans among the populace were ordered to practice their crafts for the benefit of their new Mongol overlords. Thus the deaths of the 450 merchants in the Mongol trade caravan and the execution of Chingis Khan’s emissary to Gāyer Khan were avenged.