With all that established

Rome therefore remains pagan and strong, though it does, as it did in real history, split into two realms, each with its own Emperor -- a new Greek-speaking one with its capital in Constantinople, and the old western one with its capital in Rome. At times in my book, as in the real reality, the relationship between the two Empires is friendly and close; at other times they look upon each other with a barely veiled hostility, and sometimes the hostility is not veiled at all. But in our world the western empire will fall beneath the onslaught of the barbarian hordes late in the fifth century; in the world of my novel it goes on and on and on, century after century.

With all that established, I faced one of the most difficult tasks in writing an alternative-history novel: how to let the reader know where the point of divergence from real history occurs, without simply addressing the reader directly and straightforwardly spelling the thing out. I solved this with a little prologue, set in the Roman year 1203 -- our year 450 -- in which two elderly historians, meeting by chance in the library, engage in a pleasant conversation in which one of them wonders what course history might have taken if that obscure Egyptian tribe, the Hebrews, had succeeded in getting out of Egypt and spreading their subversive cult's beliefs through the Empire. His colleague is unimpressed. "'Well,' said Aufidius, suppressing a yawn, 'all that is sheer fantasy, you know. None of it happened, after all.'"

And off I go into the first long section of the book. It takes place in 1282 -- our year 529, by which time in our world the Empire of the West had already fallen -- and is intended to depict life in the city of Rome itself with the western realm very much a going concern. That chapter is followed by one, set about eighty years later, in which a Roman who has been sent into exile in the torrid and unpleasant land of Arabia discovers a potential threat to the safety of the Empire, an intensely charismatic prophet named Mahmud who is preaching a monotheistic religion with an extremely powerful appeal. Mahmud is planning to spread his creed to all neighboring lands, and my Roman shrewdly takes steps to have the man done away with before he can cause serious trouble.