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Sec. iv]   THE POSITION OF THE `YANG BARRIER'   623

Nan-hu, for those wishing to approach Tun-huang by this route from the side of Lop or Tsaidam, is the first place where water and grazing are obtainable in abundance, and by holding Nan-hu it would be possible to ward off practically any raid which might be attempted upon Tun-huang from the Altin-tagh. The distance to be covered from Anambar (Khanambal), the last place where some real grazing is available, is so great, and the intervening glacis of stony and gravel ` Sai'so utterly devoid of resources, that no force coming from that side could move upon Tun-huang without giving its animals first a good rest at Nan-hu. Considering what we know about the Jo Chiang and their nomadic successors, the Chung-yün, the importance for the Chinese of controlling this route by the ` barrier ' established at Nan-hu is obvious."

The barring of the route at Nan-hu was greatly facilitated by the natural obstacles which the ground to the west and south of the oasis presents. In both directions, but especially westwards, extends a wide area of high dunes, which also cover the slopes of the low ridges cropping up over the underlying gravel glacis (see Maps Nos. 79. A, B. I ; 75. c, D. 1). Progress among these dunes is distinctly troublesome on the track between Somoto and Nan-hu,'6 and practically impossible for horses further north, where in May, 1907, the high sands frustrated Surveyor Ram Singh's attempt to reach Somoto from the terminal basin of the Su-lo Ho. Thus Nan-hu was naturally defended from the west, where, in the absence of such protection, Hun raiders and others might have attempted to turn the western flank of the Limes line by getting round the marshy basin just mentioned. We shall see further on that the protection thus afforded to the flank chiefly determined the policy of making the Limes end at that basin. We find this great belt of dunes west and south-west of Nan-hu specially mentioned, in the report of the Chinese mission which passed here in A. D. 938-39, as the ` Sands of Yang kuan '.17 The use of this designation is of particular interest because it indicates the survival, at a relatively late period, of a genuine local tradition connecting the ` Yang barrier ' with Nan-hu.

It only remains for me briefly to notice what I can gather from accessible Chinese records about the name Yang given to this ancient frontier-station. In the Han Annals and the historical texts elucidated by M. Chavannes I can find no explanation of the origin of the name. But in the Tun Huang Lu, the short treatise on the Tun-huang region, translated by Dr. Giles,'$ which I have mentioned above, we read the following curious passage : ` West of the city [of Tun-huang] is the Yang Barrier, which is the same as the ancient Yü-mên (Jade Gate) Barrier. It was because Yang Ming, when Governor of Sha-chou, resisted an Imperial warrant for his arrest and fled over the border by this gate, that it afterwards came to be known as the Yang Barrier. It connects China with the capital of Shan-shan, but the natural obstacles of the route and its deficiency in water and vegetation make it difficult to traverse. The frontier-gate was afterwards shifted to the east of Sha-chou.' In judging of the critical value which may be attached to this statement, it should be remembered that the little treatise which furnishes it was composed probably close on a thousand years after the two frontier-stations on the routes leading westwards from Tun-huang were first

Natural defences of Nan-hu.

Name of

Yang kuan

explained in

Tun Huang Lu.

of A. D. 938-42 west of Tun-huang is described in the record extracted from the Pien i lien, Rémusat, Ville de Khotan, pp. 78 sq.; cf. also Richthofen, China, i. p. 536, note; Ancient Khotan, i. p. 178 ; above, p. Sao.

16 The report on the Chinese mission to Khotan of A.D. 938-42 specially emphasizes the dread in which the Chinese of the Tun-huang region held the bold raids of the Chungyiin, then supposed to be descended from the remnants of the ancient Ylieh-chih, the later Indo-Scythians ; cf. Rémusat, Ville de Khotan, p. 78.

It is worth noting that at the time of that mission the Nan-hu hsicn was probably already abandoned ; see above, p. 621, and Giles, J.R.A.S., 1914, p. 712.

'a Cf. Mr. Littledale's brief account of this march, Geogr. Journal, 1894, iii. p. 458.

" See Rémusat, Ville de Khotan, p. 78. By the river Tuhsiang, there said to be passed west of Sha-chou and before the ' Sands of Yang kuan', the Tang Ho must be meant.

18 See Giles, J.R.A.S., 1914, pp. 715 sqq.; also his re-translation, J.R.A.S., 1915,11 45-

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