The iconic red gates of China's Forbidden City feature golden door nails with specific rules regarding number and color. These were symbols of hierarchy exclusive to the royal family during the Ming and Qing dynasties.

Visitors to the Forbidden City in China’s capital city might find it hard to ignore its magnificent red door, but there is more to the entrance than its beauty. The golden door nails not only neatly line up, they were exclusive to the royal family and cannot be seen everywhere in China. In the Ming (1368–1644) and Qing (1644–1912) dynasties, door nails were a symbol of hierarchy, and are bound by strict rules. Firstly, the number of door nails must be odd because in traditional Chinese culture,....