About the middle of the twelfth century the report reached Europe of the conversion as early as the beginning of the eleventh century of the Khan of the Karaït, a Tartar tribe, lying south of Lake Baikal, with its headquarters at Karakorum. The Syrian Christians, through whom the report came, misinterpreted his Mongolian title Ung-Khan as denoting a priest-king named John, and it was this distant Eastern potentate who came to be known in Europe as Presbyter Johannes or Prester John. It was the Syrian Christians who, in their desire to outvie the boastful arrogance of their Latin neighbours, together with many apochryphal tales invented a letter from this dignitary to some of the sovereigns of Europe, including the Pope. Equally fabulous seems to have been the report to Alexander III of a physician named Philip, that this shadowy personage desired reception into the Roman communion; for Alexander's answer apparently met with no response. In 1202 the tribe of the Karaïtes became the vassals of the great conqueror Ghenghiz Khan, who is said to have added to his wives the Christian daughter of the last Ung-Khan of the tribe. The kingdom of Prester John, however, lived on in fables, of which the best known relates how the Holy Grail, the cup consecrated by Christ at the Last Supper, had withdrawn from the sinful West and found refuge in this distant land. [Sidenote: The Mongols in Europe.] The conquests of Ghenghiz opened an entirely new chapter in the relations between Western Europe and the Mongols. Ghenghiz himself before his death in 1227 overran China, Central Asia, Persia, and penetrated as far west as the Dnieper. His successors entered Russia in 1237, conquered the Kipchaks about the Caspian Sea and pursued their fugitives into Central Europe, defeated the Poles, ravaged Saxony and Silesia, and overran Hungary (1240). It was fortunate for Europe that the death of the Great Khan in 1242 caused the Mongol leaders to withdraw their forces back to the East. The chief result of this Mongolian raid was that 10,000 Kharizmians fleeing before the Tartars entered the Egyptian service, and in 1244 captured Jerusalem for the Egyptian Sultan. At the time of the Tartar invasion the Papacy was vacant; but in 1243 Innocent IV was elected, and in 1245 at the Council of Lyons a crusade was mooted. But the renewal of the papal quarrel with Frederick II so far added to the general indifference that no crusade was possible. Louis IX of France alone forced his nobles to take the vow and fulfil it. [Sidenote: Innocent IV's missions.]