Gillian Bradshaw does late Romans, and does them very well. I loved her novel The Bearkeeper's Daughter about Theodora, from the pov of her illegitimate son, and she wrote one set in late Roman Britain as well, contemporary to Marcus Aurelius.

Carolus Magnus as That Guy? That would be great, if you'd do it. Speaking of synthesis, do you know we had a Byzantine empress later, Theophanu? The Ottonians were a dynasty of powerful women. Otto I. was married to Adelheid who became regent after his death. Otto II was married to Theophanu - and she's called "empress" not "consort of the emperor" in the documents, which was really unprecedented - who as mentioned was a Byzantine princess - and died young, so she ruled for her son Otto III. Who also died young.