Decline and Fall mostly covers the Byzantine Empire. If what you want is the Western Empire up to about 500 AD, Decline and Fall won't give you much. In fact, Decline and Fall mostly just alludes to the period before Constantine.

I personally don't know much about the Eastern Empire, but it's what little I've come across hasn't hooked me. I find the Rise and Fall of the Republic far more compelling.

Maybe my impressions are off.

When I think of the Western period I'm thinking of how types of kings made them who they would be, of the potential and idealism (even if apocryphal) of the likes of Cinncinatus and Furius Camillus. The formative trauma of Brinnus, and the machinations of early expansion, gradual as it was, but full of novelty. Then the trauma of Hannibal followed by their sudden explosion into the Middle Sea filled with foreshadowing of the coming fault-lines of economic imbalance and polarization. Scipio provides some early though incomplete precedence upon which Marius would extrapolate, upon which Sulla, Sertorius, Pompey and Caesar would extrapolate. So to as Tiberius Gracchus' noblest intentions tragically leading down a road of perdition through Saturninus, Clodius and Milo, and others who would oppose them. The whole arc of it just feels like some fundamentally new kind of history is colliding with the present.

The sense of gotten of the Byzantine period is that, while full of intrigue and complex events, that history had in a sense stopped, and that everyone was just conniving or crusading or consolidating to hold onto what they already had. Maybe there are compelling stories of reformers and firebrands there that I've simply missed because I haven't looked enough. But it seems to me to it is more of the same stagnant empire that was ossified by Diocletian as the Dominate; from Republic to Principate to Dominate to ... just more of the same. I'm curious to see if anyone thinks I'm just dead wrong about that?