Turkish-Tibetan, and Mongol-Tibetan (or Mongol-Turkoid Tibetan), (7) Tibetan. The Chinese use four terms to express these relative quantities, which may be called X, Y, Z, and A. The term "X," pure and simple, never under any circumstances refers to any but Tibetans (of whom at this time the Chinese had no recorded knowledge whatever except by name); but "X + Y" also refers to tribes in Tibetan regions. The term "West Y" seems to mean Tibetan-Tartars, and the term "North Y" seems to mean Mongoloid- Tunguses. There is a third Y term, "Dog Y," evidently meaning Tartars of some kind, and not Tibetans of any sort. The term "Z" never refers to Tibetans, pure or mixed, but "Y + Z" loosely refers to Turks, Mongols, and Tunguses. The terms "Red Z", "White Z," and "North Z" seem to indicate Turks; and what is more, these colour distinctions--probably of clothing or head-gear-continue to quite modern times, and always in connection with Turks or Mongol- Turks. The fourth term "A" never occurs before the third century before Christ, and refers to all Tartars, Coreans, etc.; but not to Tibetans: it need not, therefore, be discussed at present. The modern province of Sz Ch'wan was absolutely unknown even by name; but several centuries later, as we shall shortly see, it turned out to be a state of considerable magnitude, with quite a little imperial history of its own: probably it was with this unknown state that the bulk of the Tibetans tried conclusions, if they tried them with China at all. Be that as it may, the present wish is to make clear that at the first great turning-point in genuine Chinese history the whole of north and west China was in the hands of totally unknown powers, who completely shut in the Middle Kingdom; who only manifested themselves at all in the shape of occasional bodies of raiders; and who, if they had any knowledge, direct or indirect, of India, Tibet, Turkestan, Siberia, Persia, etc., kept it strictly to themselves, and in any case were incapable of communicating it in writing to the frontier Chinese populations of the four buffer states above enumerated. CHAPTER IV THE SOUTHERN POWER But the collapse of the imperial power in 771 B.C. led to restlessness in the south as well as in the north, north-western, and north-eastern regions: except for a few Chinese adventurers and colonists, these were exclusively inhabited by nomad Tartars, and perhaps some Tibetans, destitute of fixed residences, cities, and towns; ignorant of cultivation, agriculture, and letters; and roving about from pasture to pasture with their flocks and herds, finding excitement and diversion chiefly in periodical raids upon their more settled southern and western neighbours.