The unified Roman empire effectively fell during the Crisis of the Third Century. It was too large to be ruled from a single capital. The capital would always b

The unified Roman empire effectively fell during the Crisis of the Third Century. It was too large to be ruled from a single capital. The capital would always be too far to respond effectively to threats at distant borders, or from disloyal generals ruling over distant provinces. Diocletian eventually managed to stabilize the empire, but it was almost always split into 2-4 parts afterwards. The western capital was moved from Rome to Mediolanum, while Diocletian chose Nicomedia in the east as his capital. Rome was never a capital again, and eastern parts of the empire tended to be more important than western parts, because they were wealthier and more densely populated.