《资治通鉴·隋纪·隋纪五》
后来，张衡监督营建楼烦城，因炀帝巡游楼烦城，张衡才得以谒见炀帝。
久之，衡督役筑楼烦城，因帝巡幸，得谒帝。
Later, Zhang Heng supervised the construction of Loufan City. Because Emperor Yang toured Loufan City, Zhang Heng was able to meet Emperor Yang.