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Sec. in TOWERS T. ix, x AND THE MARSH SECTIONS OF THE LIMES 663

the Khara-nôr lake. - The defensive border line has been carried here across a succession of marshes and small lakes which fill the ends of depressions running from the south towards the Su-lo Ho ; further on it skirts the wide lagoons and marshes into which the Su-lo Ho expands after leaving the Khara-nôr, as well as this larger lake itself. The first-named section may be described as reaching from the lake near T. x to T. xvii ; the second may be said to extend thence to near the eastern end of Khara-nôr, marked by T. xxüi. b.

There can be no possible doubt, after the close survey I was able to effect both of the line of the Limes and of the ground over which it had been carried here, that this alignment of the wall and watch-stations was chosen with set purpose and much care by the old' Chinese engineers in order to supplement their line by natural defences, and thus to save labour of construction as well as effort in its guarding. It is fortunate, and at the same time significant, that we find a distinct reference to this point in the important document from T. vi. b, Doc., No. 6o, already mentioned,3 which has preserved for us some record of an imperial edict directing the establishment of a military colony, evidently in the territory of Tun-huang. It clearly enjoins the governor of Chiu-ch`üan or Su-chou entrusted with the execution of the edict, ` to examine the configuration of the places. Utilizing natural obstacles, a rampart is to be constructed in order to exercise control at a distance'.

Of the careful adaptation here prescribed of the line of the Limes to the configuration of the ground and of the intelligent use of natural obstacles to strengthen or replace it I could not wish to find more striking illustrations than those provided by the remains of the wall and watch-stations along the sections of the Limes mentioned above. But as soon as I began their exploration from the lake near T. x, I found my task complicated to no small extent by peculiar topographical features. Seeing how closely the Limes itself, and consequently also my archaeological labours concerning it, have been affected by the local topography, it will be convenient briefly to explain its general characteristics before I describe in detail the observations and finds connected with individual stations.

Some time before, when I first followed the route from Lop to Tun-huang, I had noticed lakes and marshes north of it in the depressions which are frequently passed from this point onwards. But only when I set out on the preliminary reconnaissances here particularly necessary, and proceeded to visit each ruined tower I had seen before rising far away to the north over what then had looked a uniform dead level of gravel desert, did it become clear how broken the ground was over which the border line of wall and posts had been drawn. What had seemed a flat plain, extending to the gravel glacis of the bare and lifeless hill chain of the easternmost Kuruk-tagh, now proved to be in reality a succession of low and somewhat narrow gravel-covered plateaus separated by winding depressions. A reference to the map in 'Plate 33 will help to illustrate this intricate configuration of the ground. It resembled a strongly developed coast-line, with flat tongues of land left between a complex system of bays and inlets. They all distinctly recalled the ` coast-line ' of the great marshy basin on the south-west flank of the Limes, though the features observed there had been of a somewhat simpler type and the differences of level more marked. J ust as there, it was easy to see that the depressions, ordinarily running from south-east to northwest, had been originally produced by the erosive action of the drainage descending from the foot of the mountains south of Nan-hu, which in earlier periods was obviously far more abundant than now.

The marshes which now fill great portions of these depressions, and chiefly those lying to the north of the caravan route, are fed by springs receiving subsoil drainage from the glacis of the

3 See above, p. 647.

Natural defences of Limes line.

Limes adapted to configuration of ground.

Gravel plateaus and marsh-filled depressions.