《北史·列传·卷八十五》
太武帝认为西域虽然已经在汉代通使，有所求时低声下气而来，无所想时就傲视怠慢皇命。这是他们自知地处偏远，王朝大军不能到达的缘故。
太武以西域汉世虽通，有求则卑辞而来，无欲则骄慢王命，此其自知绝远，大兵不可至故也。
Emperor Taiwu believed that although the Western Regions had sent envoys during the Han Dynasty, they would come humbly when they had requests, and ignore and treat the imperial orders with contempt when they had nothing to ask for. This was because they knew that they were located in a remote area that the imperial army could not reach.