《汉书·传·匈奴传上》
那时汉朝边塞各郡的报警烽火十分精明，观望仔细，入侵边境的匈奴人很少顺利的，因此很少再入侵边塞。
是时，汉边郡烽火候望精明，匈奴为边寇者少利，希复犭已塞。
At that time, the alarm fires in various prefectures along the Han border were very accurate, and the observation was very careful. The Huns who invaded the border rarely went smoothly, so they rarely invaded the border again.