Just a huge question

I keep remembering that there was apparently an ancient fortress that was supposed to be superior to any modern building, does anyone know what it was called? I'm drawing blanks here. I'm thinking of using its name or making a reference to it for my first story.

Comments

[StormDancer]

There was Orsini or maybe you're thinking of Gibraltar?
I mean, there's been a LOT of fortresses over the centuries, some of which are still somewhat viable even to this day.