What is the meaning of the sentence "decisive battle against the top of the Forbidden City"

The top of the Forbidden City is the highest place in the palace. In ancient times, it meant to stand higher than the emperor and fight a decisive battle, symbolizing the status of the master.

The Top of the Forbidden City is a martial arts film jointly produced by China Film Group Corporation and Yongsheng Film Company, directed by Liu Weiqiang and starring Andy Lau, Ekin Cheng and Nick Cheung. On February 3, 2000, the film was released in Hong Kong.

The film tells the story of the struggle between the major martial arts schools, but it turns out that this struggle is actually a conspiracy of Ye Gucheng. When Ye Gucheng's plot was discovered, he and Ximen Chuixue fought to the death at the top of the Forbidden City, and finally Ye Gucheng died by Ximen Chuixue's sword.