Diocese of Annonarian Italy

Italia was the name of the Italian Peninsula during the Roman era. It was not a province, but the territory of the city of Rome, thus having a special status. Italy and its borders expanded over time, until Augustus finally organized it as an administrative division consisting of eleven regions (from the Alps to the Ionian Sea). The islands of Corsica, Sardinia, Sicily and Malta were added to Italy by Diocletian in 292 AD. Roman Italy remained united until the sixth century, when it was divided between the Byzantine Empire and territories of the Germanic peoples. After that, Italy remained divided until 1861, when it was reunited in the modern Kingdom of Italy.

Following the end of the Social War in 88 BC, Rome had allowed its Italian allies full rights in Roman society and granted Roman citizenship to all the Italic peoples.

After having been for centuries the heart of the Roman Empire, from the 3rd century the government and the cultural center began to move eastward: first the Edict of Caracalla in 212 AD extended Roman citizenship to all free men within the imperial boundaries. Then, Christianity became the dominant religion during Constantine's reign (306–337), raising the power of other Eastern political centres. Although not founded as a capital city in 330, Constantinople grew in importance. It finally gained the rank of eastern capital when given an urban prefect in 359 and the senators who were clari became senators of the lowest rank as clarissimi.

...
Wikipedia