Not sure that amounts to “stainless,” but it is very much worth noting that the region of the world in question here has a vast and noteworthy history of fine metallurgy. This part of the world also has relatively good geographic connections to India, and that should say something all on its own.
Here’s a page from Dr. Sean Manning’s blog on a much, much earlier development in that same region regarding metal working and technical craftsmanship for reference:
…Actually, if you want something much closer to “ancient stainless,” the Iron Pillar of Delhi is a much better subject in my opinion (note the distant, but plausible geographic similarity). And of course, I learned about that one from your material!