《后汉书·列传·西域传》
到了宣帝、元帝时期，西域终于成为藩国臣下，边关不用关闭，不用再传送紧急的军事文书。
至于宣、元之世，遂备蕃臣，关徼不闭，羽檄不行。
By the time of Emperor Xuan and Emperor Yuan, the Western Regions had finally become vassal states, the border gates did not need to be closed, and military dispatches were no longer urgently sent.