168 DISCOVERY OF ANCIENT BORDER LINE CH. X
brink of a deep-cut, dry river-bed. Adjoining it I traced the foundations of a small structure, badly decayed, probably the watchmen's quarters. Fragments of iron implements, carved wood and a piece of stout woollen fabric which I picked up quickly confirmed this. Later systematic survey has proved that this was a watch-tower advanced beyond the westernmost section of the ancient protected border line.
The fodder supply carried for our ponies was now beginning to run short, and this made it imperative to gain the Tun-huang oasis, still five marches off, without undue delay. Next morning we had passed only three miles beyond where we had halted by the side of what proved the terminal bed of the Su-to-ho, when I noticed another ruined watch-tower on a gravel ridge at some distance away to the south-east. Letting the caravan move on by the well-marked track, I hastened up to the tower (Fig. 7o) . It showed the same construction as the first. On the flat gravel surface around there was no indication of other structural remains. But my attention was soon attracted by a line of reed bundles cropping out from the gravel soil close by. Following this a short distance along the plateau edge, I saw to my delight that the line stretched away perfectly straight towards another tower visible some three miles to the east and assumed the form of an unmistakable wall where it crossed a depression.
A little prospecting revealed that I actually stood on the remains of this wall. On clearing away the slight layer of drift-sand, we soon came upon a regular wall constructed of horizontal reed bundles placed at regular intervals across layers of stamped clay, the whole consolidated by permeating salts (Fig. 7 1) . On the outside, and placed at right angles
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