Italia suburbicaria (Italy "under the government of the urbs", i.e. Rome) was a vicariate of the late Roman Empire established by Constantine I (306–337).

[1] In fact, the sources of the time, such as the Laterculus Veronensis and the Notitia Dignitatum, attest that de jure Italy continued to be subdivided into a single diocese, the dioecesis Italiciana, which in turn was divided into two vicariates.

[1] Constantine, after demilitarizing the Urbe to prevent revolts and usurpations (the praetorian guard had supported Maxentius), transformed Rome's agens vices praefectorum praetorio into the vicarius urbis Romae, stripping him of all military power and making him the highest civil authority in Italia Suburbicaria.

[5][6] Cosentino, on the other hand, denies Hartmann's thesis, pointing out that in 557 the vicarii are still attested as dependent on the prefect of the praetorium of Italy and not on the praefectus urbi.

[5] By the end of the sixth century, in the Byzantine era, it appears that the vicarii were only concerned with the management of finances, having lost much of their former authority.