Rome actively sought out the Muurish Africans because they were the founts of knowledge, religion and culture. Egyptian and Ethiopian priest presided over the shrines of Isis, which were prevalent all over the Roman empire.
One also had Muurs from Africa, Ethiopia and Libya. Muurish Africans from Morocco, from Egypt, as far as the present day Nigerbend countries like Nigeria and Mali were also prominent in the Roman empire. Many were landed aristocracy like the family of Septimius Severus, (and others such as Gaius Nigrinus etc).
Engineering geniuses from Alexandria, from Thebes, Egypt and others from Kart Hadash, from Meroe, and Abbyssinia all flocked Rome because there was a sore need of them in the construction and finishing of the imperial building projects.
Black Romans carved in stone
Master stone cutters of Nubia and Ethiopia, master stone masons of Egypt and Libya, master builders of Anatolia, Cretes, Cyprus, Malta and southern Greece, all black, all children of Africa, were the real builders of the cities of the Roman Empire. It was almost comparable to how black people built the Americas, just that in Roman, those builders were celebrated nobility, whereas in the case of Americas, there were degraded as slaves. (Which is why it is generally said that ancient Romans invented nothing new and simply built on the foundations of more sophisticated but more ancient civilizations).
The point cannot be overemphasized. The Africans were foundational to the building and the expansion and the success of Rome. Thus, at the time of Septimius Severus, the African Muurs had gotten so influential and so numerous in the Empire that it was only a matter of time before they would take over the reigns of command.