From the Annals of the Oasis Kingdoms:
That season, the nomads travelled from Yiwu to the region near Anxi, establishing their encampment in the ruins of an ancient and long-abandoned town north of that city.
The armies of the Middle Kingdom made many attempts to dislodge them, sending horse riders and regiments of soldiers. But they were defeated by the nomads’ greater knowledge of the desert and its ways. The horse nomads ambushed their patrols and left the survivors for the vultures.