Athena Chu: Cheng Gu.
Interpretation: ① City Wall. The city refers to the wall of the inner city, and the country refers to the wall of the outer city: Lake Biwa shines on the city. ② Generally refers to "city" or "city": battlements and warehouses are empty, and many people are in exile.
In ancient times, inner cities and outer cities generally referred to cities or cities.
Tang Du Mu's "Epang Palace Fu": "Vertical columns and horizontal thresholds are more than nine soil (battlements)."
Yao Nai (Nai) in Qing Dynasty: "Looking at the sunshine (city wall) at dusk, the water is picturesque."
"Yutai Xinyi's ancient poem is Jiao Zhongqing's wife": "Dongshe has virtuous women and is graceful."
From the Spring and Autumn Period to the Ming and Qing Dynasties, all the capitals of other dynasties had battlements except Xianyang of Qin Shihuang. The walled city system is an urban construction system of "building a city to protect the monarch, building a country to protect the people" (Wu Yue Chun Qiu) and "being a city inside and a country outside". There are generally three walls in Beijing: Miyagi (Ouchi, Forbidden City), Imperial City or Inner City, and Outer City (Guo); There are two walls in Fucheng: Zicheng and Luocheng.
There are two forms of battlements: