Every visitor to the Forbidden City in Beijing must have seen the rows of round nails on the gate of the Forbidden City. Some people will think, what's the use of these round nails?

Of course it's useful.

This kind of round nail installed on the gate is called "door nail". At first, the use of door nails was to reinforce. At that time, a gate was often made up of several boards. As time goes on, it will inevitably disperse. To avoid this phenomenon, people put wooden belts on the inside of the door panel and add a row of wooden nails from the outside to make the door more secure.

Later, the row of door nails gradually arranged in order, and the material also changed from wood to iron and copper, playing a role in fire prevention.

In the Ming and Qing dynasties, the gates of the rich and noble families used copper nails, and gold was also distilled on the copper, showing a golden yellow color, which contrasted well with the red gates. At this time, the door nail has decorative significance and beautification function.

Before the Qing Dynasty, there was no regulation on the number of door nails. You can use as many as you want. However, in the Qing Dynasty, this could not be done. The Qing Dynasty had clear regulations on the number and arrangement of door nails. The illegal use of door nails was suspected of arrogance and might be punished. At this time, the door nail has the function of representing the grade.

The Forbidden City, called the Forbidden City in the Qing Dynasty, was where the emperor lived. Therefore, the gate of the Forbidden City adopts the highest grade nine way door nails, that is, nine rows and nine columns, with a total of 81 door nails.

It is recorded in the Great Qing Congress that "the palace gates are all built on the foundation, covered with yellow sulfur glaze, and equipped with gold nails." "The four gates on the inner wall outside the round hill of the temple are all made of red leaves, with nine gold nails in the vertical and nine in the horizontal."

Why nine rows and nine columns? This is because nine is the pole of the number of Yang, the largest in the number of Yang, symbolizing the highest position of the emperor.

However, it is puzzling that the Forbidden City Meridian Gate, Shenwu Gate and Xihua Gate are all equipped with nine door studs, but Donghua people use eight rows and nine columns, with only seventy-two door studs. What's the reason?

One theory is that the Donghua Gate is the gate through which the coffin passes after the death of the emperor. It is the "ghost gate". At the same time, life is yang, death is yin, odd number is yang, even number is yin, so the Donghua Gate has one row less nails, and even number is used.

However, this argument does not hold water. Because the emperor went out for patrols, sometimes he also went to the Donghua Gate. It can't be considered that the Donghua Gate is only for the emperor's funeral.

In addition, the Qing Dynasty clearly stipulated the material and quantity of the door nails used by princes, princes, princes and other officials: "The prince's mansion system has five main doors, nine vertical and seven horizontal door nails." "The male door nails are seven in both vertical and horizontal directions, and the number of male door nails below the marquis decreases to five, all of which are made of iron."

The princes, princes, bailes, shellfish, Zhenguo dukes, Fuguo dukes and other palaces cannot use more than the material and quantity of the door nails, otherwise it will be against the system and will be punished.

Here is another interesting story. Emperor Qianlong liked to play chess, so he came to Prince Yu again to play chess. Prince Yu suggested that if he lost a game, he would pull out a doornail; When Emperor Qianlong lost a game, he was given an extra salary. Emperor Qianlong readily agreed. As a result, after ten sets, the two killed five to five. Prince Yu pulled out five nails and got five salaries.

Emperor Qianlong felt that he was losing something: I took five useless door nails, but lost the real gold and silver! So he said, "I won't lock your door nails or reward you. I will allow you to increase the wall of your mansion by 3 feet!" There are certain standards for the height of the wall. It is also an honor to allow you to increase the wall of your mansion. Prince Yu thought about it and happily agreed to increase the wall of his mansion by 3 feet.

Of course, Prince Yu later learned the intention of Emperor Qianlong, which actually imprisoned himself more tightly. Since then, the saying "the house of Prince Li's Mansion, the wall of Prince Yu's Mansion" has been spread among the people in Beijing.

This folkloric story is of course fictional, but it reflects the restrictions on the number of door pegs used by the Prince's Mansion.