In other word: Has anyone tried slapping some metal plates in their castle walls, whether permanently or temporarily?
Or has metal been used in other ways for that purpose?
I’ve heard that as the Mongol expanded and incorporated new technologies from annexed populations, they came to possess many new artillery engines, such as counterweight trebuchets, that can defeat any defensive walls, including some that utilized metal plates as wall reinforcement.
However I can’t seem to find anything that mention such practice, whether common or rare, permanent or temporal/desperate.
Agreeable-Western-25 t1_irrj2mm wrote
Castles have some iron fittings e.g. portcullis spikes, sconces etc. In order to plate wall with metal that could withstand e.g. a trebuchet or ballista you're talking battleship thickness. Stone and timber were much cheaper and easier to transport for repairs. Considering as well a suit of armour would have cost $100,000 in today's money because metal wasn't mass produced it wouldn't have been economically viable to plate a building and good luck finding enough ore without modern mining methods.