eastern extremity of the Pei-shan to the oasis of Mao-mei. This extends from the junction of the Su-chou and Kan-chou rivers for some distance down their united course known as Etsin-gol by its Mongol name. Beyond the northern end of this narrow cultivated belt the Limes wall with its watch-towers comes down close to the left bank of the wide river-bed. Obviously the line must have had its continuation in the sandy desert stretching east of the Etsingol. But when we came back in June from the Etsin-gol delta the summer heat had become too great to permit of tracking the line farther on this waterless ground.
It is here that the route of invasion from the Mongolian steppes cuts through the ancient border line drawn by the Chinese when they first occupied the passage land to the north of the Nan-shan. The ruined forts of imposing size and evident antiquity which we found here on both banks of the river were, no doubt, intended to guard the gateway for invasion here presented. One fort built with clay walls of exceptional strength looked an exact counterpart of the ancient frontier post of the `Jade Gate' as located by me seven years before on the Limes in the desert west of Tunhuang.
As we moved down by the Etsin-gol from that last outlying Chinese settlement we found the sandy bed of the river nearly a mile wide in places but absolutely dry at the time. Only at rare intervals could water be obtained from wells dug in deep hollows below the banks. Some ninety miles below Mao-mei the river passes through a low rocky spur thrown out by the Pei-shan and then spreads out in a delta extending for some r r o miles to the north before it terminates in a line of brackish lakes and marshes.
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