Problem solved

I suppose they mean using the same techniques and materials they used back then.

Sometimes it's not just what it's made of, but also the structure of it. We're still not entirely able to replicate the nanotubes found in Damascus steel or that Starlite heat resistant material that was lost with its inventor.

Or the unbreakable glass of ancient rome (which could be ground breaking if we could replecate it)

Strictly speaking, we are able to reproduce Damascus steel in its constituent parts but we don't know how they made it all together (nor can we do it through any method). And if the Starlite thing is the same as what I'm thinking, I'm pretty sure there was no proof that it existed either because he was so paranoid that someone was gonna steal it.