The time when “EVERYONE” in Europe was White does not exist. They knew what people with brown skin looked like because they were there. They knew what “Africans” looked like because they were there, and they weren’t “they”, they were us, or you.
The oldest surviving” image that depicts Saint Maurice as a Black African was carved in the for the Cathedral of Magdeburg. Maurice was an Egyptian from Thebes in Upper Egypt. His Egyptian origin is stressed by the Coptic Greek name "Maurikios