CAP (CROWN)

The 'cap of a crown' is the cap which fills the inner space of a modern crown. While ancient crowns contained no cap, from mediæval times it became traditional to fill the circlet with a cap of velvet or other such cloth, with a base of ermine.
While the precise reason for the inclusion of a cap is unknown, two reasons are often given:

★ to add to the visual impact of the crown, while showing off the golden circlet to maximum effect;

★ to keep a monarch's head warm in drafty mediæval buildings during long coronation ceremonies or public events where crowns were worn.
Not all crowns however contained cloth caps. Some caps were metallic and heavily jewelled.