《旧唐书·列传·卷五十三》
从朔方到云中，边境线长达数千里，在要害地段开拓旧城，有的地方则自己制定规则，开拓边域各数百里。
自朔方至云中，缘边数千里，当要害地开拓旧城，或自创制，斥地各数百里。
From Shuofang to Yunzhong, the border line is thousands of miles long. In the key areas, the old cities were opened up, and in some places, their own rules were formulated to open up hundreds of miles of border areas.