We have pretty good clarity that Septimius Severus wasn't racially African. His parents were of Italian and Carthaginian descent. To portray a Roman emperor -- with no further specification -- as black is to intentionally misrepresent the historical record. I use the term "race or ethnicity" because this was the language Bard used when referring to its rewording of my prompt. That other cultural portrayals of emperors have likewise been inaccurate doesn't mean I should be satisfied with the same from Imagen, especially when there are competing image models which will dutifully synthesize an image of much higher correspondence to my request.
I didn't say ”imperial concept”, its an “age of imperialism” concept (though, in retrospect, “age of exploration” is when it started, it just really gained salience in the age of imperialism; though whether it was ~1300 or ~1600 years too late to apply to him isn’t a big difference.)
At least in the late Roman Republic, there was absolutely a concept of race that unified e.g. the various Gallic tribes, or differentiated the peoples of the Roman East. It's always been a sociopolitcal concept. But the Romans were aware of e.g. North Africans versus dark-skinned Africans.
