It was only in 49BC that Ravenna was given full Roman status, yet by the time of Augustus not long after it was a major naval hub for the Adriatic fleet. Here is a rough map of the ancient city, if you'd like to peruse. Let it be known that in 402 when it became the capital, it was given new defensive walls and was also considered safer than Rome, because it was originally set amidst marshland (as opposed to now).

Ravenna by the 5th century had actually grown to flourish. It had a great deal of art and mosaics and when Honorius transferred there were sumptuous palaces constructed (though most of the extant archaeology lies in Churches -- though contains some gorgeous mosaics). But it was a city worth keeping and a city worth using, as Justinian shows when he used it as capital of the West in 540.

Sources: Oxford Classical Dictionary and The Art of Ravenna in Late Antiquity by Stuart Cristo p. 17-29