I frequently visit a an example of a vitrified fort in Angus. Possibly the reason why vitrified forts are only found in Scotland is because 'vitrification' of stone walls was a Pictish technology. Instead of cement, the picts realised that burning wooden beams in the core of the ramparts would cause the stones to fuse together as one. archaeologists would tend to argue that this would make the stone more brittle.........yes it would, but we aint talking about one stone, we are talking about thousands of them fused together to form a defensive barrier.