Speaking of the imperial city of Beijing, many people don't know much about it. According to Hou Renzhi, a famous scholar, "The rigorous planning of Beijing's old city and the magnificent palace architecture are unparalleled in the feudal imperial city in the world." "At the beginning of the old city planning, the Forbidden City was surrounded by the imperial city, and there was an inner city outside the imperial city. Later, the outer city was built in the south of Dacheng, so there were inner cities and outer cities. There are nine gates in the inner city and seven gates in the outer city, each with its own towers and different shapes. There are urns and watchtowers outside each door, which are also different. At the four corners of the inner and outer cities, an arrow tower was built, so the shape of the city defense was suddenly prepared, which was not available in any previous capital. " From this point of view, since the Ming Dynasty, the Imperial Capital has had three and a half laps. The center of Miyagi is the Forbidden City as the imperial palace, and the second circle is the imperial city. Outside the imperial city is the inner city, and the outermost half circle is only in the south, which is the outer city.
The imperial city wall was not expanded until the Qing dynasty, but it was repaired many times. According to the unified records of the Qing Dynasty, the circumference of the Imperial Capital is about eighteen miles, and the total length should be 3,304 feet. Qing Hui Dian records that the imperial city wall is 3656 feet. The walls of the imperial city are different from those of the inner and outer cities. In fact, it is a wall 18 feet high, 6 feet wide and 5 feet 2 inches wide. It's all brick, with a small amount of broken masonry in the middle, red chalk on the wall and yellow glazed tiles on it. The Qing Dynasty perished and entered the Republic of China. Due to the need of municipal engineering, the Imperial City Wall was demolished one after another in the mid-1920s, leaving only a section in the south, that is, the "Tiananmen Red Wall" standing from the east side of Tiananmen Gate to the intersection of Nanhe Street and the west side to Fu You Street. The other three imperial city walls and three gates are gone. However, when Beijing was carrying out municipal construction in Xihuangchenggen, the foundation of the city wall was dug up. When Huangchenggen Ruins Park was built, the old base site was also dug up at the original site of Dong 'anmen.