This is to demonstrate the supremacy of imperial power and royal majesty, and also to prevent people from bringing knives and other things that threaten the emperor's life. Therefore, a "dismounting monument" will be set up at the entrance of the Forbidden City. Everyone must walk there.
The dismounting stele reads, "Officials, dismount at this point." This is to show the strict hierarchy of feudal ethics. Except for the emperor, no one is allowed to enter the Forbidden City on horseback or in a sedan chair. As the highest level of the ruling class, the emperor has supreme power. No one is allowed to resist the imperial power. The Forbidden City, as the emperor's office and accommodation, is inviolable. Therefore, when officials or relatives of the emperor arrive in front of the dismounting monument, they should walk into the palace to show respect for the imperial power and the emperor himself.
Secondly, dismounting and walking is also to prevent people with ulterior motives from bringing weapons into the palace to assassinate the emperor, which is a kind of protection for the emperor. In many movies and TV dramas, we can see such a plot. A person enters the palace to meet the saint, and suddenly takes out a dagger from his arms. Therefore, after dismounting in front of the Dismounting Monument, you will be subject to a security check by the royal guards to see if you are carrying daggers and other weapons. According to regulations, civil and military officials are not allowed to carry weapons when going to court or entering the palace to see the emperor, otherwise they will be severely punished.
But in fact it is not that no one can ride a horse or ride a sedan in the Forbidden City. In order to reward officials, win over people's hearts and highlight their importance, the emperor gave many people the privilege of riding horses and sedan chairs in the Forbidden City. This is a way to win over courtiers without any cost, and the officials are grateful and feel it is a supreme honor. For example, Qianlong stipulated that older officials could go to court in sedan chairs, which reflected the emperor's love for all civil and military officials.