Ravenna is not at the top of most people's lists of places to visit in Italy--it certainly wasn't on mine--and I only added it to my trip at the strong urging of online friends. I'm glad I did. The city is not only a pleasant place to eat and walk--it has an amazing treasure in its Byzantine mosaics, dating from the 5th century AD.
Ravenna was an important naval port in Roman times, but its greatest significance came late in the game. From 402 to the fall of Rome, it was the capital of the Western Roman Empire, and within a hundred years or so became the Italian capital of the Byzantine (Eastern Roman) empire. Its glorious mosaics and beautiful churches date from that era, which lasted until the Lombard conquest around 700.
The Basilica of San Vitale is only one 8 UNESCO World Heritage sites in Ravenna, but it is perhaps the most lavishly decorated, except possibly for the tomb of Galla Placidia next door. One unique feature in the slideshow below: the glowing rectangles are actually sheets of marble shaved as thin as window glass. They bring suffused light into the room without any direct illumination.
A combination ticket is available for all 8 sites, which can be seen in a day, but are better in two. Useful information for Ravenna HERE