Xun Zi Han Bing: "The drums advance, and the golden sound retreats." Drums give orders to attack, bells ring orders to retreat. There is a legend about the origin of "beating drums to sound gold" for your reference: the Yellow Emperor made a leather drum when he was fighting against Chiyou. He hunted an animal named Kui in Liubao Mountain in the East China Sea of China. It is shaped like a cow, with a bluish-black body and a faint light. It has no horns on its head and only one foot. This animal looks like electricity and cries like thunder. It is very powerful and magnificent. At that time, the Yellow Emperor was overwhelmed by its sound, so he skinned it and made it into eighty drums, and let Empress Xuan Nv beat the drums herself. Suddenly, it sounded like thunder, and it spread for 500 miles. This is the origin of later generations' "beating drums to advance, ringing gold to retreat". Another way of saying it is from yin and yang and five elements. The ancient five elements correspond to East, West, North and South respectively, namely, Dongmu, Xijin, Huo Nan, Beishui and Middle Earth. However, due to the underdevelopment of ancient science and technology, the troops in the war generally withdrew before sunset. At sunset, the sun sets in the west, so there is a saying that the golden bell closes the moon. That is, blowing the horn of the sunset means that the soldiers go back to the city to rest.