《汉书·传·匈奴传下》
况且以往我们谋取西域，控制车师，建设城郭，设置都护，统领保护三十六国，一年花费的钱财数以百万计，难道是为了害怕康居、乌孙越过白龙堆而侵掠西部边境？
且往者图西域，制车师，置城郭都护三十六国，费岁以大万计者，岂为康居、乌孙能逾白龙堆而寇西边哉？
Moreover, in the past, we planned for the Western Regions, controlled Che Shi, built cities, established protectorates, commanded the protection of thirty-six countries, and spent hundreds of millions of money a year, was it because we were afraid that Kang Ju and Wusun would cross Bai Longdui to invade the western border?