I think this also displays the ignorance of the Left. When the Romans thought "African", they thought the lighter skinned people of the Sahara and Mediterranean, Berbers, or the descendants of Phoenician colonists and the like. "Aethiopes," or Sub-Saharan Africans, were an incredibly rare sight in the Roman Empire. Sorry, lefties, Septimius Severus was not a black man. I hate to say it, but throughout the majority of European history, Black people have been a footnote. Arabs and Turks have had far more of an affect than Sub-Saharan Africa, yet they aren't the emphasis in diversity hires when it comes to historical dramas.
And, as a final note, when we first start really recording black people in Britain, there were about 400 of them in Tudor England. This was out of a population of four million.