Zhongnanhai is in Xicheng District. It is collectively known as the "three seas" with Beihai. When the Zhonghai was opened in Jin and Yuan, the South China Sea was dug in the early Ming Dynasty. The Qing Dynasty and Beihai were jointly called Xihaizi and listed as a forbidden garden. Entering Zhongnanhai, many people are confused. Why is Zhongnanhai called "the sea"? It is obviously a lake!