The Regio III Lucania et Bruttii, the third of the Regions of Augustan Italy, bordered to the east and north with the Regio II Apulia et Calabria, to the north-west with the Regio I Latium et Campania, while to the south it was enclosed by the Ionian Sea and Tyrrhenian Sea and went as far as Fretum Siculum (the Strait of Messina).

In Lucania et Bruttii the frequentation of the itinerary maritime from Salerno to Reggio, already attested by the Siculum iter of Lucilius, and later used by Cicero in the summer of 44 BC, evidently suggests to Diocleziano planners the annexation of the Picentino area and an overall arrangement of the territory centered on the two poles of Salerno and Reggio. In this way, the movement of populations and inhabited areas towards the coast is consolidated, while the land route along the Via Popilia is downgraded to serve short-distance connections or for access to inland areas.

Between the end of the 3rd century and the beginning of the 5th century Salernum was the administrative center of the province and the seat of the Corrector (governor).