Tang poetry says that "there is no reason for people to go out of Yangguan in the west". Where does "Yangguan" refer to?

Yangguan is the name of the border pass set by the Han Dynasty, so it is located near the antique beach in the southwest of Dunhuang County, Gansu Province. Located at the throat of the Silk Road, Yangguan is one of the important passes leading to the western frontier in ancient times. According to the geography monograph of Yuan and County in Tang Dynasty, Yangguan was called Yangguan because it was south of Yumen and south of the ancients was Yang. After the demise of the Tang Dynasty, the northern minority regimes became independent, the Silk Road was gradually abandoned, and Yangguan was gradually depressed or even disappeared.

Yangguan, located at the western end of Hexi Corridor, is opposite to Yumenguan in the north. It is not only a military fortress, but also a commercial artery. Since the Han dynasty, many dynasties have sent troops to guard this place as military strongholds. During the Han and Tang dynasties, when the country was strong, it was common to join the army or go to Yangguan, but at that time, the west of Yangguan was still barren and the scenery was quite different from that of the mainland. Of course, soldiers who went to war may never come back, and businessmen and travelers who went to the west also survived. Relatives and friends can't help but travel long distances to taste the hardships and loneliness of going alone for Wan Li. How many soldiers guarding the border in history have bid farewell to their loved ones here; How many businessmen, monks, envoys and tourists have embarked on a long journey here; How many literati and poets face the sunshine and sigh and write immortal poems? Therefore, the farewell of Yangguan is more saturated with people's rich and profound friendship, so Yangguan has been endowed with profound humanistic significance for thousands of years. It is not only a geographical term, but also a cultural symbol.