古时候，人们为了防御外来的进攻，在重要的城市四周会围起坚固的城墙。但是城墙围起来以后，城市和外面也不能断了联系啊，这就得靠城门。所以，城门必须有两个功能，首先是作为出入城市的通道，同时，它还有对外防御的作用，必须高大、坚固。

In ancient times, the Chinese people erected hard and durable city walls around important cities to defend against outside attacks. After these city walls were in place, however, contact still needed to be maintained between those inside and outside the city—which is where city gates came into play. The city gate thus needed to have two functions. First, it had to serve as a passage for entering and leaving the city. Second, it had to protect against outside threats. For this reason, China’s ancient city gates needed to be tall and sturdy.

　　城门的主要建筑是城楼。城楼与左右的城墙相连，城楼中间是城门洞。

The main structure of a city gate is the city gate tower. The tower is connected to the city wall on either side, with a tunnel located beneath it.

　　中国很多的城市现在还保留城墙和城门。比如北京的城门，有句话叫“内九，外七，皇城四”。

Today, many of China’s cities have still retained their city walls and city gates. The phrase “inner nine, outer seven, and imperial city four” is used to describe the city gates of Beijing.

　　“内九”指的是内城的九个门。按顺时针方向，分别是东边的东直门、朝阳门，南边的崇文门、宣武门和正阳门，西边的阜成门和西直门，北边的德胜门、安定门。

The “inner nine” refers to the nine gates of the inner city. Listed in clockwise order, these gates are Dongzhimen and Chaoyangmen on the east side; Chongwenmen, Xuanwumen and Zhengyangmen on the south side; Fuchengmen and Xizhimen on the west side; and Deshengmen and Andingmen on the north side.

　　“外七”是指外城的七个城门。按顺时针方向，分别是东边的东便门、广渠门，南边的左安门、永定门、右安门，西边的广安门和西便门。

The “outer seven” refers to the seven gates of the outer city. Listed in clockwise order, these gates are Dongbianmen and Guangqumen on the east side; Zuo’anmen, Yongdingmen and You’anmen on the south side; and Guang’anmen and Xibianmen on the west side.

　　“皇城四”，指的是东边的东安门、南边的天安门、西边的西安门、北边的地安门。

The “imperial city four” refers to Dong’anmen on the east side, Tian’anmen on the south side, Xi’anmen on the west side, and Di’anmen on the north side.