Let me try to add these "old" books
by Robert Graves
I, Claudius (1934) and the sequel Claudius the God and his Wife Messalina.
LatinandGreek has it in his to read list.
by Gary Jennings
Raptor (1993), The novel treats actual historical events, the fall of the Western Roman Empire and Theodoric's assassination of Odoacer among them.
by Mika Waltari
The Etruscan
The Roman sequel to The Secret of the Kingdom about the early days of Christianity.
I had great pleasure in reading all of them. I time I reread them several times.
Recently I read with pleasure a non fiction book by Edward N. Luttwak "The grand Strategy of The Roman Empire", easy, entertaing and very interesting. It's a book of 1976.
Years ago I read by Jerome Carcopino "La vie quotidiane a Rome a l'apogee de L'Empire" flunked all the accents, as I consider myself Quebecquois. It is a book of 1941. I was not even born then. Not even a spark in my mother's eye.