What is the most prominent feature in the pattern of Beijing's old city?

Beijing has always been called an ideal capital by feng shui experts. The Xishan Mountain in the west is Taihang Mountain. Dujun Mountain in the north is the Yanshan Mountains, belonging to the Kunlun Mountains. The two mountains meet at the south entrance of Beijing (the south entrance is a battleground for military strategists), forming a semi-circular mountain bay that spreads to the southeast. The Beijing Plain surrounds this mountain bay. The terrain slopes slightly from northwest to southeast. Sanggan River, Yanghe River and other rivers meet here to form Yongding River. Geographically, "Liao Tuan is in the east, Taihang is in the west, Shuomo is in the north, the army is behind, and the Central Plains is in the south." Strategies conducive to development and control.