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 or 81 studs, as the number nine represented the supremacy of the monarch.
Other titled personages, princes and barons had fewer studs on their gates,
such as 9 rows 7 each, 7 x 7 or 5 X 5; those who had lower ranks had studs made of iron.