Mongol rulers of the Yuan Dynasty destroyed the Jin capital. The sumptuous palaces were set ablaze, the fires burning for more than a month. In 1624, Yuan rulers abandoned the site of the former Jin capital and constructed a new city known as Dadu, centered in the Jin emperor’s auxiliary palaces. The new city walls, with a perimeter of 30 kilometers, measured 21.6 meters at the base and 16.7 meters at the top. This was the embryonic form of present–day Beijing.

In 1368, Zhu Yuanzhang, the first Ming emperor, attacked and captured the Yuan capital Dadu and established his new capital at Nanjing. His son Zhu Di renamed Beiping (Northern Peace) Beijing (Northern Capital) in 1403, and in 1421 officially made it the capital of China. In the middle of the Ming Dynasty, plans were made for a new encircling wall outside the old walls. Work was begun on the southern city wall, but lack of finances brought work to a halt at the completion of the eastern and western corner towers. This resulted in a truncated pyramidal shape for the inner and outer cities.

Economic construction and development since 1949 has necessitated the gradual demolition of the city walls. Twenty–eight radial roads connect the city center and suburban scenic areas, factories and schools. The old city walls remain only in name; row after row of multi – story buildings have already been built on their ruins.

The standing city gates, however, are wonderful reminders of the past. Not counting the Hepingmen (Peace) Gate, the Fuxingmen (Rejuvenation) Gate and the Jianguomen (National Foundation) Gate, the city of Beijing at one time had 20 gates. Today, the four gates of the Forbidden City–Meridian Gate (Wumen), Gate of Divine Prowess (Shenwumen) and East and West Flowery Gates (Donghuamen and Xihuamen) still retain their original form. Of the gates in the old inner walls, only the southern gate, Zhengyangmen, remains intact.

Originally, the outer side if each city gate was frontier by fortifications. An essential part of the overall city plan, they took the form of secondary gate towers just outside the gates. Connected to the main city wall by semi–circular curtain–walls, they resembled earth ware jars and were known as “urn walls” (wengcheng). Xizhimen is an example of a square “urn wall.”

The main function of the “urn walls” was to strengthen defense capabilities of the garrison troops protecting the city. “Urn towers” on top afforded protection to archers inside while allowing them to shoot freely. In the event of a surprise attack, the main gates were quickly closed to prevent the enemy from entering the city. When the defense prepared for an engagement with the enemy, they first concentrated their forces within the “urn walls.” If the enemy entered the “urn walls,” they became an easy target for the troops at the main city gate. There were usually one or two temples within the “urn walls,” where people used to pray to the gods for protection.

(china.org.cn)