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Sec. i] GEOGRAPHICAL FEATURES OF LOWER SU-LO HO BASIN   58!

Kua-chou, north-westwards to the foot of the easternmost Tien-shan, and gains it at the ancient Road

oasis of Hâmi, or Kumul. This route, too, as we have already had occasion to note, is of early An hgil

date, its passage through Hâmi being definitely mentioned in the Later Han Annals.8 Through to Hâmi.

changes largely physical, which we had to consider repeatedly in connexion with Lou-lan, this route

became in Tang times the main artery of traffic between China and Central Asia, and remains so

to the present day. I shall have to discuss it and its possible variants on the east and west in

a subsequent chapter.sa Here it may suffice to point out that it is solely on account of its position

where the present highway leaves the Su-lo Ho, to strike across the desert ranges of the Pei-shan

to Hâmi, that the collection of modest villages now grouped as the ` district ' of An-hsi figures

more prominently in our maps and in Chinese administrative classification than the far greater and

richer oasis of Tun-huang.

It was different in Han times, when Tun-huang was famous among the four ` commands ' of Importance

Ho-lasi, or Western Kan-su, side by side with Liang-chou, Kan-chou, and Su-Chou.° Tun-huang huan;n-

derived its importance for the Chinese then from the great advantages which its geographical

position and resources offered, and which are easy to recognize even now when the line of the great Central-Asian route has finally shifted northward. It represents the largest area capable of con-

tinuous cultivation whiéh can be found now, or is likely to have existed in historical times, between

Su-chou and Khotan, a distance of over 1,200 miles. Compared with its extent of arable land, even now a compact stretch over twenty miles long from south to north and about sixteen miles at its

widest part, the oases that lie eastward to Su-chou are small, and those in the Lop region insigni-

ficant. It is easy to realize how great in consequence was the value which Tun-huang possessed for the Chinese at the time of their first advance into the Tarim Basin, and while the most direct

route via Lou-lan remained open. It was incrèased by the fact that this important base of supplies for the movements of troops and trading caravans lay so far west, at the very point where the

Lou-lan route entered the great wastes of desert ground wholly devoid of human sustenance.

Tun-huang owes its comparatively large area of cultivation wholly to the fact that it occupies Physical an extensive and easily irrigated alluvial fan at the very debouchure of a considerable river which at Tu conditionsnaffords an abundant and, at the critical seasons, reliable supply of water. As I have had occasion huang.

to emphasize elsewhere, there exists a very close affinity between practically all the physical features of the lower Su-lo, Ho Basin and those of the Tarim Basin. Both are inland drainage

areas of exactly analogous climatic conditions, and probably, as mentioned above, at an earlier period had their lowest depressions linked up.10 It is a necessary result of this close agreement in essential geographical factors that here, as in the Tarim Basin, the extent of cultivation is entirely dependent upon the natural facilities for irrigation.

At Tun-huang these conditions are more favourable than anywhere else between Su-chou in Irrigation

the east and Khotan or Kucha in the west. The Tang Ho, or river of Tun-huang, is a river facilities of

Tun-huang.

of considerable volume, which breaks through the main range of the western Nan-shan and, as Captain Roborovsky's fine map on the scale of 1 : 840,000 shows, drains a high mountain area to the south quite as large as, if not larger than, that drained by the Su-lo Ho. Among the ranges feeding it there are several which raise their crests well above the permanent snow line, and must carry extensive snow beds and even glaciers of some size. This is certainly true of the range which we surveyed on its northern slope between Shih-pao-ch`êng and Ch`ang-ma, and which, as Map No. 84 shows, has peaks over 20,000 feet high. Its drainage to the south flows mainly

8 See above, pp. 329 sq., 563 ; Chavannes, T`oung pao, 1907, pp. 156, 169.

8a See below, ch. xxvllt. sec. i.

° Cf. Chavannes, T'oung pao, 1906, p. 258, note 2 ; Documents, p. v ; Wylie, J. Anthrop. Inst., x. p. 2 2.

10 Cf. Desert Cathay, i. 535 sqq.; above, pp. 55o sq.