Ruins of Desert Cathay 180 - Ruin of ancient watch-tower T.vi a, on western flank of the Tun-huang limes, seen from south - The tower is built on an eroded clay ridge, and on right overlooks a depression with Toghraks and reed beds. Stein determined that the several detached towers to the south-west of the end of the wall were positioned as look out stations covering a gap between the Su-lo Ho delta and the huge sand dunes to the west.