Where is Saibei in the poem?

Saibei in poetry refers to a geographical term of China in the past, which is rarely used now.

Plug refers to frontier fortress and fortress. The so-called plug here is equivalent to the Great Wall of Ming Dynasty today. Taking this as a boundary, the northern part of the border has been blocked, hence the name Saibei.

Now it is the area north of the Great Wall of China, including Inner Mongolia Autonomous Region, northern Gansu Province and Ningxia Hui Autonomous Region.

Please adopt it, thank you!