The main entrances to ancient palaces, temples and mansions have doors with studs arranged in rows. Like other decorations on traditional buildings, the studs served to indicate ranks in the feudal hierarchy.

Door studs go back a long time in history. To keep off aggression, heavy city gates were built and braced on the surface with iron plates, which were fastened on by means of studs. This system lasted for thousands of years.

The door studs on the gates of the Forbidden City were made of brass and plated with gold. Lustrous, they add to the splendour and magnificence of the imperial palace. All the gates used by the emperor have 9 x 9 studs, as the number nine represented the supremacy of the monarch. Other titled personages, princes and barons had fewer studs on their gates.

An interesting question arises with regard to the Donghuamen gate of the Forbidden City which, unlike the other principal entrances, have 72 studs instead of the usual 81. The explanation lies in a historic event. At the end of the Ming Dynasty, the capital fell to Li Zicheng, leader of a famous peasant revolt in 1644. And it was by Donghuamen that Chongzhen the last Ming emperor left the palace and then hanged himself at Jingshan (Hill of Prospect, popularly known as Coal Hill). The Qing house which replaced the Ming regarded Donghuamen as inauspicious, decided to use it for the exit of imperial hearses and cut down the number of its studs at the same time.