> If the Romans had written a warning on a building in plain Latin about how entering it would unleash the wrath of the gods, we would have absolutely no problem to understand it.

Today we can, the privileged few in our current golden age of technology and widespread literacy. Take the non-privileged masses in the US and elsewhere, they wouldn't know what to do with Latin script written on a building, even now. They wouldn't know how to translate it on the web, they wouldn't even know it was a warning.