138 WESTERN FLANK OF THE LIMES CH. LXII
permeation with water had produced on ruined sites by the salt-impregnated shores of Lake Baghrash.
On May 2nd, while excavation at the towers continued under Chiang-ssû-yeh and the Naik, I made a long day's reconnaissance with a few mounted men along the ancient route to the north-west. It furnished definite proof that, though there had been no extension of the wall in that direction, yet the towers I passed on my first approach to Toghrak-bulak in March had been constructed at the same time as the Limes proper. Evidently these were meant for watch-posts from which fire signals, such as the records of the Limes so often mention, could be sent on in advance to the detachments guarding the wall. Their position suggested that the deep-cut old river bed, now completely dry, near which these outpost towers were built, had then still received water from the Su-lo Ho, or had, perhaps, served as its main flood-bed. Now the river was confined to the narrow Toghrak-bulak bed, filling it so completely that we had to descend some distance before we could find a place shallow enough to cross. Its width there was over forty yards, the water being close on three feet deep, and flowing with a velocity of about two yards per second.
The following days were devoted to the exploration of the line of watch-stations which stretched far away to the south-west along the edge of the great marshy basin. The distances at which they were placed from each other, ranging from four to six miles, showed clearly that they were meant mainly as signalling-posts along a line and not for the purpose of warding off inroads. The objects which the wall was intended to serve along the front of the Limes was here secured by the impassable nature of the marshes westwards. Yet even thus the links of the chain of posts could not have been kept so far apart, with the consequent saving in trouble and cost, had not the configuration of the ground offered ideal positions all along for conspicuous signalling-stations.
As a look at the inset map A shows, the bare gravel-covered plateau marking the foot of the glacis of the
mountains here stretches out a succession of finger-like ridges of clay. These project into the wide marsh-filled
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