A poem "Send Yuan Twenty-one Xi" should be familiar to most people. It appeared in our primary school textbooks and was once an ancient poem that we had to recite. The rain in the early morning moistened the dust of the land, the inn of the inn, the branches and leaves of the inn, and a new leaf Sincerely advise friends to drink a glass of wine, and it is difficult to meet their relatives when they go out to the sun. Unlimited ambition and lofty sentiments are reluctant to go to the frontier, and friends will soon be far away and will soon be unwilling to see each other. In the information transmission with underdeveloped traffic in ancient times, after a farewell, we will never see it again, because it will be a distant place, and people who have been there will have little chance to come back. So where is the sunshine we often refer to today?

In fact, the Yangguan in Wang Wei's poems is an antique beach in Nanhu Township, 70 kilometers southwest of Dunhuang City in Hexi Corridor today. This is an important pass in ancient times. Because of the terrain here, it is an important treasure in ancient military strategy, especially in the Han Dynasty to resist the invasion of northwest nomadic people.

We also had the Silk Road in ancient times, and this place was on the Silk Road. It can be said that it is the hub of transportation and its strategic significance is very important. Because of the peculiar and dangerous terrain, it is often a battleground for the royal family.

In fact, there were two very important strategic locations in ancient times, namely, Yangguan and Yumenguan, but these two places were also south and north, which played an important role in southern Hebei, because these two places were important connection points between the Central Plains and the Gobi Desert in the northwest, and they were very similar, which not only had important significance, but also played an important role in the Silk Road and even in the communication between Asia and Europe.