What are customs clearance documents?

During the Han and Tang Dynasties, Yangguan and Yumenguan were the gateways between the Central Plains Dynasty and the western countries. In order to prevent the northwest Xiongnu, Turkic and other forces from threatening the security of the Central Plains Dynasty, since the Western Han Dynasty, local officials began to issue customs clearance documents in Yangguan as vouchers for entering and leaving Yangguan. This certificate is similar to the later passport to go abroad.

At that time, camel caravan business travelers, including some monks, wanted to go to the western regions, and they had to go through customs clearance at Yangguan before they could go to the western regions. Countries in the western regions also attach great importance to the official seal issued by a captain in Yangguan. In the classical novel The Journey to the West, there have been many references to customs clearance documents.

Whether people from the western regions come to Han or people from the Han Dynasty go west, they have to go through strict verification and affix the nursing seal of Yangguan before they can be released. Once the photo is in hand, it can be unimpeded. So later, languages such as "caring" and "caring more" spread, and later generations extended "caring" to mean caring and convenience.