These expeditions, if they failed in their main purpose, were at least the means of giving to the world much curious information concerning the inhabitants of the Great Tartary. "Prester John," or, to call him by his right name, Ung-Khan, was the most powerful Tartar prince of his day. Genghis, then called Temoujin, when a very young man, repaired to the court of Ung-Khan to seek aid to repress disturbances among his own tribes, and soon became commander-in-chief of Ung-Khan's armies, in which capacity he displayed the high military qualities which afterwards made him master of nearly the whole civilised world. He was a great favourite with the Khan, and all went on smoothly until the unlucky day when Ung-Khan's daughter fell in love with young Temoujin. The course of true love did not run smooth with him, for his rivals being fired with enmity, began to plot against him with the Khan, who in time yielded to their instigation, and betrayed his best friend. Temoujin remained true to his colours long after he lost the confidence of the Khan; but the discovery of a deeply-laid plot against his life at length brought him to an open rupture with his sovereign. They fought a pitched battle between the rivers Tolla and Kerlon, probably at a short distance eastward from the present Urga. Ung-Khan's forces had greatly the advantage in numbers, but the Khan was no match for his accomplished general. Temoujin gained a decisive victory. The Khan escaped from the field of battle, but was soon afterwards killed, and his dynasty destroyed. Temoujin now found himself master of the situation, and was installed at Kara-Korum in 1206, under the title of Genghis-Khan.