"Yangguan" and "Yumenguan", one south and one north, are located at the western end of Hexi Corridor. Since the Han Dynasty, it has been an important gateway for the mainland to the western regions (one of the two passes that must be passed after leaving Dunhuang). Therefore, it is said in the Tang poetry that "there is no reason for people to go out of Yangguan in the west" and "the spring breeze is only Yumen Pass". The ancients regarded the two passes as the watershed between China and foreigners, and regarded the west of "Yangguan" as a poor and barren land, so the content of poetry was mostly farewell, and the emotional tone was mostly desolate and depressed.
Frontier poems in a broad sense are not limited to the western regions, but also include other regions. For example, "the smoke of the Han family is in the northeast. In order to repel the barbaric invaders, our generals left their families behind." Secondly, it is not limited to the theme of parting and homesickness, but also includes the description and impassioned expression of frontier fortress scenery. For example, "the desert sand is like snow, the Yanshan moon is like a hook", "Who knows that you don't suffer from the side court, but you still smell sweet when you die" and so on.