​Metal loop protruding from wall of medieval tower basement

Metal loop protruding from wall in basement of medieval tower

Does anyone know what this is? It is situated over seven feet high in the basement of a tower built in the 14th century. The loop part is about a foot or more in diameter. I’m told the basement had a solid fuel stove in it during the Victorian era to heat a nearby public building. Once that was removed, the basement was used as a school room until the seventies. Now it’s a storage room.

We are baffled so any suggestions are welcome.