1. If you're interested in Roman history I would recommend Colleen McCullough's seven-volume The Masters of Rome series, which begins with Marius and Sulla and ends with the victory of Octavian to become first emperor. The series spans the late Republic, the fall of the Republic and the beginning of the Empire. If your knowledge of Roman history begins with Romulus and Remus being raised by wolves and skips to Julius Caesar, it's an accessible way to catch up on a lot.
2. Robert Graves' I, Claudius; Claudius the God and his Wife Messalina; and Count Belisarius. The latter is about Justinian's great general; Graves is no fan of Justinian, the last emperor to rule over both halves of the empire, but IMO the plague had more to do with Justinian's woes than anything he did personally.
3. Two novels by Gore Vidal: Burr, in which Burr and not Hamilton is the hero; and Lincoln. Vidal also wrote other historical fiction, but I found them boring and preachy.
4. I've only read two of Jeff Shaara's books — Gods and Generals and The Glorious Cause, but I expect to read more.