Very early French Louis XV era fireback.
Firebacks served a couple of purposes. The first and perhaps the most important was to protect the wall at the back of the fireplace. Unlike modern construction, early fireplaces were susceptible to the destructive impact of fire. Placing a sheet of cast iron (a fireback) would go a long way to mitigating this vulnerability. In addition to protection the fireback would also provide a comfortable radiant heat. While the fire is burning in the hearth the fireback absorbs a great deal of heat. Once the fire dies out the fireback will release its absorbed heat into the room. Another purpose of the firebacks was aesthetics. It is very common to see designs and themes cast in to the plates. Some of the more common designs found are coat-of-arms, mythical, or romantic scenes.
This 17th century French Louis XV era fireback depicts a bird perched on a ring and shows definite signs of its age.