Three characteristics recommended this book to me: 1) I am a fan of Roman history 2) I love SF short stories 3) Robert Silverberg is one of my favorite authors. With this combination, I figured I couldn't go wrong and bought this book on a whim without looking at Amazon's ratings, which I have come to rely on increasingly. I'll detail why all 3 of these characteristics failed this book and forced me to rate it 1 star, the lowest rating I have ever given a book. Normally, I don't finish books that bad but my mistake was to take too few books with me on my 3 week vacation (which was a Danube river cruise followed by a week in Constantinople/Istanbul since my hobby is visiting all the current countries that made up the Roman Empire at it's greatest extent). Therefore, I didn't have enough books to read and, once I finished everything else, I had to read this book or nothing during my cruise.
1) I expected Silverberg to be more knowledgeable about Roman history. Reading this book, my illusion disappeared quickly but as I plowed through this incessant book, I expected that he would delve further into Roman history than tossing off a few place names and the barest outlines of the empire's history. Ostensibly, Silverberg visited a few well-known Roman sites like Tivoli and Capri since he constantly refers to them but the problem with that is he, well, constantly refers to them.
2) The SF extrapolations and even simple plot elements are virtually non-existent. These "stories" are more vignettes with the last few pages wrapping up what plot elements there are.
3) Silverberg's writing is well-crafted but his characterization is thin and his plots, as I mentioned above, don't exist.
If you like Silverberg, I strongly recommend avoiding this book and buying some of his excellent work such as Nightwings, Dying Inside, At Winter's End, Kingdoms of the Wall, etc. If you like Roman History, read Tacitus, Suetonius, and even Procopius. If you like Alternate History about the Roman Empire, read Harry Turtledove's Krispos Trilogy, Videssos series, or Agent of Byzantium. Turtledove is a professor of Byzantine/Roman history and a master of alternative history. His worst efforts look good next to this mess.