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Sec. i] THE EXTENSION OF THE ' GREAT WALL' BEYOND TUN-HUANG 723

protect themselves against the inroads of the Hsiung-nu, or Huns, and thereby first created the famous ' Great Wall '. As then established, it extended from Shan-hai kuan, on the Gulf of Liao-tung, westwards as far as Lin-t`ao, corresponding to the present prefecture of Min, in the extreme south of Kan-su and about i 10 miles south of Lan-chou.2a

It was not until a century later that the ' Great Wall' received an extension to the north-west, notable both for the boldness of its far-flung line and the significant change in its purpose. In Chin Shih Huang-ti's border wall a policy of consolidated defence had found its expression. The construction of the lines of the Limes, carrying the ' Great Wall ' about a thousand miles further and almost to the easternmost edge of the Tarim Basin, was meant to serve a new policy : this took the offensive and definitely aimed at expansion into Central Asia. We have already had more than one occasion to refer to the far-reaching results of Chang Ch'ien's memorable Central-Asian mission (138-126 B.c.) under the great Han Emperor Wu-ti.3 Originally undertaken for the sake of securing possible allies against the Hsiung-nu in the Yüeh-chih, the later Indo-Scythians, whom the Hsiung-nu had driven from their old seats on the Kan-su marches into Central Asia, this mission first revealed to the Chinese the commercial importance of the great western civilizations. It also showed clearly that the geographical and political conditions prevailing in the Tarim Basin made it possible there to open for Chinese trade a direct and safe route of access to Ta-yuan or Farghana, Sogdiana (K`ang-chü), and the Oxus regions.

Chang Chien's report to the Emperor, as recorded in the C/f eu Han shat, rightly emphasizes the fact that communications with the Ta-hsia or Bactria were at the mercy of the Hsiung-nu on the north and of the Chiang or Tibetans on the south. Only in passing straight between them lay safety from attacks of both nomadic nations.4 In the light of our present geographical and historical knowledge it is easy to realize fully the soundness of Chang Ch'ien's recommendation and of the Imperial policy which soon gave effect to it. As soon as the Chinese had gained the gap of Tun-huang, where contact between Hun and Tibetan raiders ceased, there stretched westwards before them the absolute desert of Lop, difficult to cross but safe from human attack ; and Chinese policy has always been readier to face the dangers of nature than to fight elusive barbarian foes. Beyond the Lop Desert the two great routes of the Tarim Basin lay open, leading westwards to the desired goal. The great stretches of desert ground and the oases between them, which had to be passed through on these routes, were equally unsuited for nomadic occupation. The small but thoroughly civilized settlements established in the oases could offer no serious resistance to aggression in any case. In fact, they were bound to welcome effective Chinese control, which would assure protection from inroads of troublesome neighbours across the mountains to the north and south-east and bring lucrative trade in its train.

To Tun-huang, at the same time gate and base for the Chinese advance into the Tarim Basin, nature had provided only one main route from China on the south-east, but that remarkably easy and safe. Its line leads along the foot of the well-watered north-eastern and northern slopes of the great Nan-shan range, and it is followed to this day by the great high road connecting China proper with Chinese Turkestan for purposes of trade and administration. Between Lan-chou and Liang-chou the easternmost extension of the main Nan-shan is crossed by an easy pass, open for

Northwestern extension of Great Wall'.

Chang Ch'ien's report on route into Central Asia.

Easy high road along north foot of Nan-shan.

4a It is of interest to note that, as M. Chavannes has duly pointed out, this Great Wall of Ch'in Shih i-Iuang-ti is clearly marked in the Chinese map engraved A. D. 1137 but based on earlier sources, which he edited in B.E.F.E.O., 1903, R. 214 sqq.

We shall see further on that the same map also marks the

Han Limes east and west of Tun-huang; see below, p. 735, note 3o.

Cf. above, pp. 336, 553, 580. For a full translation of the Memoir of Chang Ch'ien, contained in the Former Han Annals, see Wylie, J. Anthrop. Inst., x. pp. 66 sqq.

See ibid., x. p. 67.