[hnfong]

Not the GP but I'll be more concrete in the other direction.

The Roman Empire is located in Europe, is more recent than "time immemorial", and I'll claim that they didn't regard the various barbarians in Europe outside its sphere of influence as culturally unified with them.

[eru]

It depends a bit on what we mean by 'time immemorial'. See https://en.wikipedia.org/wiki/Time_immemorial for some possibilities.

In a legal context, 'time immemorial' is often much, much more recent than the Roman Empire, even the Eastern part.