In 212, when the Edict of Caracalla gave the Roman citizenship to all the people within the empire regardless of their ethnicity or social status, Italy began to decline in favor of the provinces.

The following crisis of the Third Century was a period in which the Roman Empire nearly collapsed under the combined pressures of invasion, civil war, plague, and economic depression.

In 284, the rise of Diocletian began a series of reforms to restoring civil order.

He divides the Empire into four parts and several dioceses, the so-called Tetrarchy.

Though still keeping Rome as the official capital, he chooses two other residences for the Augusti: Maximian, who is responsible for the West, is installed at Milan in northern Italy, in order to prevent German invasions; Diocletian establishes himself at Nicomedia, in Anatolia and close to the Persian frontier, in order to keep watch on the East.