This is an antique cast bronze door rosette or escutcheon plate. Escutcheons, roses, or rosettes were used prior to door escutcheon plates. They are usually used in combination with keyhole covers or escutcheons in a coordinating design. These later gave way to "Combined Escutcheon Plates", which is a plate with both the doorknob hole (or thimble) and the keyhole cutout.