[Kleon]

Until the first quarter of the seventh century, Classical civilization was alive and well in the Mediterranean world. City life flourished, as did the economy and the arts. Literacy was widespread, and the works of the Classical historians, as well as the philosophers, mathematicians, and physicians, were readily available and discussed in the academies and libraries located throughout the Near East, North Africa, and Europe.

This is highly debatable. One reason the Carolingian Renaissance of the eighth and ninth centuries is so-named is because the centuries before had seen a dramatic drop in literacy and knowledge of Classical authors. Literacy was almost non-existent, and not even widespread among the clergy.

[Cicero]

There were Christian cities all across North Africa. St. Augustine was Bishop of Hippo, and even the smaller cities of his time were civilized. You get some sense of it from the earlier chapters of the Confessions.

That was the case until the Muslims led by Mohammed swept across North Africa and destroyed it all. Europe was set back by tribal invasions from the North, but those peoples then gradually were converted to Christianity and became civilized. That was not the case in North Africa and the Near East, where the invading Muslims destroyed the former civilizations and they never really recovered.