China in particular became the prey of these warlike horsemen. We hear little of them in the early days, when the Chinese realm was narrow and the original barbarians possessed most of the land. We hear much of them in later days, when the empire had widened and grown rich and prosperous, offering an alluring prize to the restless and daring inhabitants of the steppes. The stories we have already told have much to say of the relations of China with the nomads of the north. Against these foes the Great Wall was built in vain, and ages of warfare passed before the armies of China succeeded in subduing and making tributary the people of the steppes. We first hear of Tartar raids upon China in the reign of the emperor Muh Wang, in the tenth century B.C. As time went on, the tribes combined and fell in steadily greater numbers upon the southern realm. Of these alliances of tribes the first known was named by Chinese historians the Heung Nou, or "detestable slaves." Under its chiefs, called the Tanjous, it became very formidable, and for a thousand years continued a thorn in the side of the Chinese empire. The Tanjous were dominant in the steppes for some three hundred years, when they were overthrown by a revolt of the tribes, and were succeeded by the Sienpi, who under their chiefs, the Topas, or "masters of the earth," grew formidable, conquering the northern provinces of China, which they held for a century and a half. Finally a slave of one of the Topa chiefs, at the head of a hundred outlaws, broke into revolt, and gathered adherents until the power of the Sienpi was broken, and a new tribe, the Geougen, became predominant. Its leader, Cehelun by name, extended his power over a vast territory, assuming the title of Kagan, or Khan. The next revolt took place in the sixth century A.D., when a tribe of slaves, which worked the iron forges of the Altai Mountains for the Great Khan, rebelled and won its freedom. Growing rapidly, it almost exterminated the Geougen in a great battle, and became dominant over the clans. Thus first came into history the great tribe of the Turks, whose later history was destined to be so momentous. The dominion of the Khan of the Turks grew so enormously that in time it extended from Central Siberia on the north to Persia on the south, while he made his power felt by China on the east and by Rome on the west. Ambassadors from the Khan reached Constantinople, and Roman envoys were received in return in his tent at the foot of the Altai range.