The city that became the capital of the Western Roman Empire in 402 CE was Ravenna.
Emperor Honorius moved the western imperial court from Mediolanum, modern Milan, to Ravenna in 402 CE. Ravenna offered stronger natural defenses because it was surrounded by marshes and connected to the Adriatic Sea. Its position also provided access to the Roman fleet and made it harder for hostile armies to attack.
Rome remained symbolically supreme, but it was no longer the regular seat of western imperial government. Ravenna continued in that role until the deposition of Romulus Augustulus in 476, and it later became the center of the Ostrogothic kingdom under Theoderic the Great.
The city’s late antique monuments preserve an exceptional concentration of mosaics. The Mausoleum of Galla Placidia, the Basilica of San Vitale, and the Neonian Baptistery illustrate the mixture of Roman, Christian, and eastern Mediterranean artistic traditions.