Sec. iii] EASTERN TURKESTAN UNDER THE TANGS 63
During that period the suzerainty of China was acknowledged by all the states which
Muhammadan invasion threatened, from Kashmir to the Oxus and Yaxartes, and even to distant Tabaristan on the shores of the Caspian Sea. Imperial decrees, royal titles, and occasional missions were intended to strengthen the princes of these states in their resistance by a kind of moral support. But the Chinese administration of the ' Four Garrisons ' was ready for more vigorous measures, whenever it was necessary to bar the Tibetans from access to the route which might have enabled them to join hands with the Arabs, their old allies. This route led through Gilgit and Yasin, the Little P`o-lü of the Tang Annals, to the Upper Oxus ; and we have already had occasion, in chapter i, to discuss in detail the expeditions which the Chinese undertook from the ` Four Garrisons ' to prevent this strategically important territory from falling into the hands of the Tibetans 37. In 722 A. D. it was the Sub-Delegate of Kashgar who, at the head of four thousand troops, succoured the king of Little P`o-1ü, and helped him to expel the Tibetans. Similarly Kao Hsien-chih, when setting out in the year 747 to wrest Little P`o-lü from the Tibetans, commenced his famous march over the Pamirs and Hindukush from Kashgar.
Kao Hsien-chih, under whose leadership the troops of the ` Four Garrisons ' in 75o a second
time triumphantly penetrated south of the Hindukush 38, was destined also to bring about the event which marked the commencement of the rapid decline of Chinese power in the ' Western Regions '. Having forcibly intervened in the same year (75o A. D.) in the affairs of the tributary kingdom of Tashkend, he treacherously put to death its ruler and excited the wrath of the people by his cupidity and oppression. The king's son stirred up the neighbouring populations against the Chinese and called in the aid of the Arabs. In the summer of 75 i Kao Hsien-chih marched against the latter and their native allies ; but his auxiliaries of the Karluk tribes revolted against him, and taken thus in front and rear Kao Hsien-chih, near the town of Talas (now
Auliata), suffered a crushing defeat, from which Chinese authority never recovered 39.
A succession of disasters which about the same time overtook the imperial arms
Yün-nan, at the other end of the empire, and the subsequent rise of a dangerous pretender to the throne, made it impossible for Hsüan-tsung and his son Su-tsung, in whose favour he abdicated in 757, to direct their attention to the exposed dominions in the West40. On the contrary, the frontier garrisons had to be denuded of troops in order to succour the dynasty threatened in its very existence 41. We have a significant indication of this in the fact that among the forces which finally recovered the Imperial capital of Chang-an (Hsi-an-fu) in 757, contingents of soldiers from the Protectorates of An-hsi, or Kucha, and Pd-ting (near Guchen) 42, from Farghana, and even from the Arabs are mentioned 43. The Tibetans, who had helped to foment these grave troubles, did not fail to turn to account the opportunity offered. From the years 758-759 onwards they gradually overran the regions of Ho and Lung, corresponding to the present province of Kan-su and the extreme west of Shan-si. From the time when they were completely established there, about 766 A.D., all direct communication between China and the Protectorates of An-hsi and Pei-t`ing was interrupted".
Concerning the final phase of Chinese dominion in these distant western territories, the Tang Annals furnish a series of brief but interesting data, which M. Chavannes has lucidly
Chinese activity outside ' Four Garrisons,'
Defeat of Kao Hsien- chih, 75r
37 See regarding these expeditions, above pp. 7 sqq.
38 See above, p. I I ; Turcs occid., p. 214, note.
39 Compare Turcs occid., pp. 142 sq., 297.
40 See ibid., pp. 298 sq.
" Compare Bushell, Early History of Tibet, p. 4 r.
42 The administrative centre of Pei-t'ing occupied a position about eighteen miles to the west of the present
Guchen, and corresponding to that of Bish-balik (' Five cities ') of Mongol times ; see Chavannes, Turcs occid., pp. r r sq. The territories governed from Pei-t'ing lay mainly north of the Tien-shan.
13 Turcs occid., p. 299.
" See Bushell, Early History of Tibet, p. 4r; Chavannes Turcs occid., p. x 14 note, and below Appendix A.