《新唐书·列传·卷一百四十一》
四镇若不能守，胡兵必临西域；西域震惊，就威慑南羌；南羌若连衡，河西必危。
夫四镇无守，胡兵必临西域，西域震则威憺南羌，南羌连衡，河西必危。
If the four towns cannot be defended, the Hu soldiers will surely come to the Western Regions; if the Western Regions are shocked, it will threaten South Qiang; if South Qiang is connected, the Hexi Corridor will surely be in danger.