This is an unidentified ,probably antique, gilt brass uniform tunic button.
I do not know what or who it represents .
Probably livery or possibly military
A castle within a shield below a crown is depicted.
A stained reverse reveals no back stamp.
The crown looks to be of a European nature.
The buttons( 22 mm diameter) is in a good condition with no real damage.
Attractive button.
A good find.
Free postage to the UK.