Short answers, pulled from the story.
Emperor Honorius moved his court from Mediolanum to Ravenna in 402 for defensive reasons: the city was surrounded by swamps and marshes, making it difficult to besiege. Its port also maintained sea connections to the Eastern Roman Empire, which was a strategic lifeline as the western provinces came under pressure.
Eight early Christian buildings in Ravenna are inscribed on the UNESCO World Heritage List under the name Early Christian Monuments of Ravenna. They include the Orthodox Baptistery, the Mausoleum of Galla Placidia, the Basilica of San Vitale, the Basilica of Sant'Apollinare in Classe, and the Mausoleum of Theodoric, among others.
The Donation of Pepin was a grant made in 756 by Pepin, King of the Franks, to Pope Stephen II, ceding authority over territory that included the former Exarchate of Ravenna. It provided the legal basis for the creation of the Papal States, after Pepin had twice invaded Italy to force the Lombard king Aistulf to surrender lands he had taken.
Dante Alighieri is buried in a tomb beside the Basilica of San Francesco in Ravenna, where his funeral was held in 1321. He spent most of his exile from Florence in Ravenna, and the city resisted for centuries all Florentine demands for the return of his remains.
Ravenna was liberated on the 5th of November 1944 by troops of the 4th Princess Louise Dragoon Guards, the 5th Canadian Armoured Division, and the British 27th Lancers. A total of 937 Commonwealth soldiers who died in the winter of 1944-45 are buried in Ravenna War Cemetery, including 438 Canadians.
Dante Alighieri spent his years of exile in Ravenna and mentions the city in the Inferno. Lord Byron lived there from 1819 to 1821 and wrote Don Juan and the Ravenna Diary during that period. Oscar Wilde, Alexander Blok, Hermann Hesse, T. S. Eliot, and J. R. R. Tolkien all wrote works set in or inspired by Ravenna.