在中国的传说中，南天门是进入天宫的第一重大门，也是帝王宫殿大门，庄严而神圣。武当山金顶的南天门建有三孔门洞，分别为神门、鬼门、人门。鬼门是象征性的门，自打建造的那天起就是封闭的——祭祀神灵的方不许鬼怪出没；神门则常年关闭，只有皇亲国戚来时才能打开；而人门是常年开启，供朝拜真武大帝的人们通行。

　　连接南天门的城墙叫紫金城。城墙由重达千斤巨大条石依悬崖走向砌垒，城墙基础厚2、4米，墙顶厚1、26米，其厚重牢固，充分体现了明永乐皇帝朱棣圣旨中“……务要坚固壮实，万万年与天地同其久远”的要求。

　　明永乐十四年，武当山天柱峰绝顶上建成了金殿。而那时，天柱峰四周并没有城墙。到1419年，明成祖朱棣下诏修建天柱峰的紫金城。整个工程历时5年完工，用巨型条石砌筑的城墙，居险临危却又坚固稳重，令人叹为观止。

　　在明永乐年间，出入紫金城是很严格的。在当时，有种说法，叫“北有紫禁城，南有紫金城”，可见，当时武当山金顶的地位相当于北京的皇宫了。

In Chinese legend, the worse is the first major temple gate, the door is imperial palaces, solemn and sacred. Mount Wudang Jinding the suspicions built three holes openings, doors were gods, ghosts door, the door person. Ghost doors are symbolic of the door, after he built is closed that day on - not allowed to worship the gods of the Phantom appear; God is perennial closed doors, only when democracy to be open; And perennial doors are open for worship Zhenwu Tati common people.
The wall is connected worse Zijin City. The walls of the huge stone weighing Flemingia according to a hell of a cliff barrier, 2,4 meters thick foundation walls, top 1,26 m thick, thick, strong, fully embodied Yongle Emperor Zhu Di of the Ming imperial "... be strong artistic works, and the earth with its Momonian long" requirements.
Ming Yongle 14 years on Mount Wudang were built Tianzhufeng extremely vague. And then, and no walls around Tianzhufeng. By 1419, Ming Emperor Zhu Di built Tianzhufeng of Zijin City. The whole project took five years for completion, with the giant, stone masonry walls, but solid Threatened Habitat prudent risk, it is magic.
Ming Yongle, Zijin access to the city is very strict. At the time, there was a kind of argument, called "Forbidden City are North, South have Zijin City" that was equivalent to the status of Mount Wudang Jinding the Palace of Beijing.