《后汉书·列传·西域传》
为传送命令骑马飞奔的驿使，一年四季连续不断；来做生意贩运东西的胡人和客商，每天都有人叩关。
驰命走驿，不绝于时月；商胡贩客，日款于塞下。
The couriers rode horses and galloped around the year without interruption to deliver orders; and the Hu people and guest merchants who came to do business and trade knocked on the gates every day.