We know that, while not an existential threat, the Berber tribes of Northern Africa were prone to raiding the frontierand coupled with their presence and the natural barriers of Africa, settlements/cities/population centres had to hug the coasts.
That's a huge systematisation to do.
In fact, the relation between the coast and the hinterland was much more symbiotic than that, the latter being often integrated somehow into a political ensemble.
I won't do all the History of Maghreb (altough if Abdallah Laroui was ever translated, that might be a good source) but this opposition is more of a narrative than the result of the historical relationship :
These weren't always peaceful, far from it, but still symbiotic at a large degree : vision of Berbers as an irremediably outlaw-ish ensemble mostly comes from the situation in North Africa in the Late Empire (but frankly, giving the raiding-fest that was Romania at this point, that's hardly a distinct Berber thing) and maybe from Ibn Khaldun's who never really consider "imperial" Berbers as Almoravids as Berbers.
An exemple of this symbiose may be the relations between
Mauri and Romans, or Umayyads and Maghrib.
I'd be really careful about such characterisation myself.
But what of Egypt, how much of the border between what was the Roman province/Ancient Kingdom of Egypt was based on outside pressure from nomads or raiders and were there any in Upper Egypt to spoke of in any capacity?
Well, the most obvious border definition was the desert : the Libyan desert is a much more vague element to draw a border on, than a series of mountains or foothills as in Roman Africa. This is more a march, a solitude if you will, that could be crossed but not directly controlled.
Generally, Romans roads are a good clue onto which parts were regularily patrolled, forming a limes. But it seems the focus was more on Nilothic peoples, even Austoriani raids focused on Cyrenaica and North Africa.
Now, you have the Libu of Ancient Egypt, but Bubastis dynasty could point that the relation may not having been about two radically distinct people, but there as well, with a more complex relationship.
