National Institute of Informatics - Digital Silk Road Project
Digital Archive of Toyo Bunko Rare Books

Ancient border line along Su-lo Ho.

River strengthens Limes defence.

Protection by waterless desert north.

584   THE TUN-HUANG OASIS AND ITS NORTHERN LIMES [Chap. XV

the bend below Yü-mên-hsien right through to the terminal basin, the line of the river was followed by the Limes wall and its chain of watch-stations intended to safeguard that road from attacks of the Huns, who then commanded the regions to the north, including the oases on either side of the eastern Tien-shan. The clearness of the broad geographical facts makes it possible for me to explain here quite briefly the advantages thus secured, without going into any of the details which we shall have to consider further on in connexion with the actual remains of the Limes.

On the east, the line of the ancient Han ` Wall ', coming from the junction of the rivers of Kan-chou and Su-chou, and carried through the desert far to the north of the great Su-chou oasis, first touched the Su-lo Ho at its bend below Yü-mên-hsien.'a Thence it followed the right, or northern, bank of the river quite closely down to a point facing the Wan-shan-tzû ridge (Map No. 83. B. 2) previously mentioned.'" By keeping this part of their line to the northern bank for a distance of about forty miles those who laid down the Limes gained several advantages. Besides securing the water-supply for their own posts—a very important consideration in this barren region—the line thus drawn kept any Hun raiding parties which might cross the Pei-shan desert on the north from gaining access to water and grazing. It similarly prevented their close approach to the cultivated area, which, as seen from the Maps (Nos. 83. B—D. 2 ; 85. A. 2), here runs down to the river's left bank. Below the Wan-shan-tzû ridge and above the little oasis of Hsiao-wan, the Limes was carried across to the left bank under the protection of high ground abutting on the river from both sides, and thence followed this bank at varying distances all the way down to the terminal basin of the Su-lo Ho.

The advantages which were obtained by keeping to the river's southern bank along this big section of the Limes, approximately 16o miles in length, were, if anything, even greater. The continuous belt of riverine marshes and lake-beds, which commences below An-hsi and extends along almost the whole of the Su-lo Ho's terminal course, very considerably increased the defensive strength of the Limes. It added to it a formidable natural barrier ; for the marshes and interlacing beds of the river make, as it were, a huge fosse, which in most places is impassable throughout the year and in others very troublesome during spring and summer. Where there were lakes or deep lagoons, it was possible, as we shall see, by including them in the line, to restrict the Limes to a chain of towers, and thus for considerable stretches to save the very serious effort which the building of the wall involved under forbidding desert conditions.

It is true that by keeping the Limes to the south of the long belt of riverine marshes such Hun raiders as could make their way from the north were allowed access to water and grazing. But against this it has to be remembered that in the desert west of the Tun-huangHami route, wells or springs of drinkable water must even in ancient times have been very rare, if they were not altogether wanting, as they are at present." Thus nature had here

1e For a brief preliminary account of this eastern section of the Limes explored in 1914, cf. my Third Journey of Exploration, Geogr. Journal, xlviii, pp. i95 sq., and the provisional sketch-map attached to it. [The new surveys are embodied in Sheets 4o, 42 of the i : 500,000 Map.]

'a For the Limes line from Yii-mên-hsien to An-hsi, see below, chap. xxvii. sec. v.

17 The track that leads from the eastern end of the Tang Ho delta below Tun-huang towards Hâmi is the last westwards of the several routes connecting the Hâmi oasis with the lower Su-lo Ho Basin on which caravan traffic is made possible by the existence of a string of wells or springs with drinkable, if brackish, water. It joins the more easterly track, now followed by the Chinese `high road' from An-hsi

to Hami, at the well of Ku-shui (Map No. 76. c. 5), and is nowhere separated from it by more than about thirty-eight miles, as shown by Captain Roborovsky's survey in the Russian Trans-frontier Map xxr.

Of the two other routes which the same map marks, on the authority of natives, as lying west of the Tun-huangHâmi route, one, according to information kindly communicated to me by Professor Pelliot, has no existence in reality, and merely represents a duplication of it caused by the record of a different set of names for the same series of wells. The existence of the second route further to the west seems to be equally problematical ; for Captain Roborovsky, who attempted to follow it from below the western end of the Khara-nor, found no wells on it for a distance of over sixty