Tāi Yāng Khān, king of the Christian tribe of Naimans, alarmed at the growing power of the young ruler, sent Alakush-Tekin, chief of the Onguts, or white Tatars, an invitation to join him against the ambitious Mongol. Alakush-Tekin immediately informed Chingiz of the Naimans’ intentions, assuring him at the same time of his own friendly feeling. Chingiz promptly marched against Tāi Yāng, who descended from the Altai to the foot of the Khanggai Mountains, attended by many allies, among whom was Tukta, king of the Merkits.[362] In the battle which took place the Naimans were utterly routed. Among the prisoners who fell into the hands of the Mongols was Tatatungo, the chancellor of Tāi Yāng, who belonged to the Uïghūr tribe, and tradition attributes to his influence the veneer of civilisation of the Mongols; and it is certain that Chingiz caused him to instruct his sons in the language, laws, and customs of the Uïghūrs.[363] Tāi Yāng Khān perished in this battle, while his son Guchluk fled by way of Bish Bālik to the country of the Gūr-Khān of Kara-Khitāy.[364] After wandering for some time and enduring great privations, he at length arrived at the court of the Gūr-Khān (1208). He was hospitably received, and the Khān gave him his daughter in marriage; but the favours showered on him did not prevent his plotting to dethrone his benefactor. He obtained permission to enlist the remnants of the Naiman tribe, and thus collected a considerable force; then he entered into a league with Mohammad Shāh of Khwārazm, and `Othmān, prince of Samarkand, who, as we have seen above, were both vassals of the Gūr-Khān. They arranged that they should attack their Gūr-Khān suzerain simultaneously, the one from the east and the other from the west. The conditions determined on were that if Sultan Mohammad should be the first to gain a victory, Almāligh, Khotan, and Kāshghar, which were in Guchluk’s hands, should be ceded to him; but if, on the other hand, Guchluk should win the initial success, Kara-Khitāy, as far as Fināket, should be delivered over to him.[365] Guchluk arrived before the Sultan, and was at first successful, but was afterwards defeated on his way to attack Balāsāghūn, and obliged to retreat. In the meantime the troops of Mohammad and `Othmān had entered Kara-Khitāy, and gained a victory over the Gūr-Khān’s general, Tanigū, near the city of Tarāz. Guchluk, taking advantage of this reverse, hurried back, surprised the Gūr-Khān, and took him prisoner, A.H. 608 (1212). Two years later the Gūr-Khān died, at a very advanced age. Guchluk, now firmly established on the throne of Kara-Khitāy, reduced his new subjects to complete obedience. He was a cruel persecutor of Islām, being himself a Nestorian Christian until his marriage with the Gūr-Khān’s daughter, when he became a Buddhist.[366]