The words "only" and "see" are skillfully used, which shows the danger of Zijingguan terrain. Among them, the word "Wei" highlights the importance of the Great Wall (or Zijingguan), which is the barrier for the Han nationality to block the northern minorities; The image of "Jian" points out that there were many banners in Zijingguan at that time.
I hope it helps you.