There are no purple buildings in the Forbidden City. Why is it called the Forbidden City?

When we walk into the Forbidden City, you will find that everything is magnificent. The Forbidden City is dominated by gold and red, without purple, so why is it called the Forbidden City? * * * There are two reasons.

The name of the Forbidden City is also a masterpiece of ancient astronomers. Ancient astronomers divided the stars in the sky into 28 stars and three walls, one of which was called Ziweiyuan, which was in the middle, so Ziweiyuan was called the Central Plains. Therefore, it is called the Forbidden City. Another reason is that my ancients called the palace of the Jade Emperor the Purple Palace, while our emperor claimed to be the son of heaven, so our emperor's palace will echo the palace of the Jade Emperor in the sky and eventually become the Forbidden City. ?