The invasion of Western Asia by the Mongols of Genghis Khan in the early part of the thirteenth century drove an unknown number of Persians and Turks to take refuge in Asia Minor. Among these is said to have been a group led by a chief named Suleiman, whose grandson Osman gave the Ottomans their name.[16] This group reached the Seljuk kingdom of Rûm, and was allowed by good custom of the time to proceed to the Christian frontier and conquer what it could. About the time of settlement tradition specifies the number as four hundred families, or 444 horsemen, a figure which has clearly been shaped with reference to the sacred number four, but which shows the belief that the group was not large.[17] The growth of this band was far more rapid than could have been accomplished by natural increase. A part of the additional membership was supplied by Turks and other Moslems of adventurous spirit who sought the fighting and booty of the border-land. But these were by no means all. The Ottoman traditions and history reveal at countless places the hospitable incorporating spirit of the embryonic nation, which rapidly increased its numbers from the Christian population by conversion, marriage, and capture, and most strikingly by the tribute tax of Christian male children. The Ottoman conquests to the eastward brought gradually into the brotherhood all the Seljuk Turks of Asia Minor, and as many as were or became Mohammedan from the various conquered peoples—Greeks of Trebizond, Armenians, Syrians, and others. The conquests in Europe converted _en masse_ some sections of Bulgarians and Albanians, who still show evidence of their origin; a very great number of individuals among the subject Christians, however, were so completely incorporated as to lose all trace of their source. Thousands upon thousands of captives from the whole of Southeastern Europe, from all of Southern Russia and Poland, from the Caucasus region, from Central Europe as far as Regensburg and Friule, and from the shores and islands of the Mediterranean were likewise incorporated; till, as a result of all this Western admixture, the ruling nationality of the Ottoman Empire, though called Turkish today, retains no physical trace whatever of Mongolian ancestry.[18] Many of its members undoubtedly have no Tatar blood in their veins; as for the rest, they are, if the above discussion be well founded, a mixture of Europeans chiefly with Turks of Asia Minor, who were themselves a mixture of the former Christian population with Seljuk Turks, while these again were a mixture dating back through countless ages of contact between the white and the yellow races. A simple computation will illustrate the matter. Osman is said to have captured a fair Greek lady named Nenuphar, or Nilufer, the Lotus-flower, and to have given her as bride to his son Orchan, the first of the Ottoman sultans.[19] From that time it became increasingly the policy of