Participants of our reading group often are interested in who in the various novels we discuss has been a real-life person. Often the Introduction or the Afterword have the answer. The Dream of Scipio has neither, so Bingley and I have done some sleuthing. Note: All Wikipedia articles should be handled with care.
The three protagonists, Manlius Hippomanes, Olivier de Noyen, and Julien Barneuve are fictional characters, although there are shades of Sidonius in Manlius, and Petrarch in Olivier.
Bingley blogged dream of scipio – roman background. I found Bishop Faustus of Riez. In the background are Sidonius and the Visigoth Euric, and there is a brief flashback appearance of Ricimer, the power behind the Western Empire at the time. The Burgundian king whom Manlius Hippomanes seeks out for help is Ricimer's nephew Gundobad, although their agreement is a fictional version of the fate of the Provence and Gundobad is more famous for his later doings.
This has been mostly covered in Bingley's post dream of scipio – mediaeval background.
Real-life Pope Clement VI engaged three astronomers or astrologers to try and discern the origin of the devastating plague. Now, the Jewish philosopher Levi Ben Gershon (Gersonides), had a great interest in astrology, so this is a short step for the novelist to have the pope call on him, the more so as Clement later decreed an end to the persecution of the Jews.
I thought Cardinal Ceccani was a fictional character, but Bingley tracked him down as Annibale di Ceccano. He and his palace also appear in the Italian version of 'Avignon' at Wikipedia. And there is his adversary (at least in the book), Cardinal Bertrand de Deaux, whose palace can be seen here.
I blogged the Sienese painter Pietro Lorenzetti earlier.
Bingley found Père Sautel, the archaeological enthusiast whom Julien meets when still a child, and who indeed dug up Roman remains in Vaison. In our novel the encounter takes place at the site of one of Manlius' villas. Lucien's mentor "Bloch" could well be the French historian of Medieval France, Marc Bloch. He became a member of the French Resistance and was killed by the Germans, a fate not much different than Julien's. And of course we all know Picasso, who has a brief encounter with the child Julia.