Italy, in Roman antiquity, the Italian Peninsula from the Apennines in the north to the “boot” in the south. In 42 bc Cisalpine Gaul, north of the Apennines, was added; and in the late 3rd century ad Italy came to include the islands of Sicily, Corsica, and Sardinia, as well as Raetia and part of Pannonia to the north.
The first major power in the peninsula was the Etruscans. From Etruria, Etruscan power spread northward to the Po River valley and southward to Campania, but it later collapsed to Etruria itself. Where the Etruscans failed, the people of Rome gradually succeeded in the task of unifying the various Italian peoples into a political whole. By 264 bc all Italy south of Cisalpine Gaul was united under the leadership of Rome in a confederacy; its members were either incorporated in or allied with the Roman state. The status of the allies gradually changed until after the Italian, or Social, War (i.e., the war of the socii, or allies) of 90 bc, when Roman citizenship was extended to all Italy. But political unification was achieved more quickly than was sentimental unity: Romans and Italici did not immediately coalesce into a nation. Cicero might talk of tota Italia, but Italy was not finally united in spirit until the time of Augustus, and Romanization was still slower in superseding local differences. In the meantime Cisalpine Gaul, which had received Roman citizenship in stages, was incorporated into Italy in 42 bc.
For administrative purposes the emperor Augustus divided Italy into 11 regions: (1) Latium and Campania, including the Volsci, Hernici, Aurunci, and Picentini, from the mouth of the Tiber to that of the Silarus (Sele) River, (2) Apulia and Calabria, including the Hirpini (the “heel” of Italy), (3) Lucania and Bruttium, bounded on the west coast by the Silarus, on the east by the Bradanus (Bradano) River (the “toe” of Italy), (4) Samnium, including the Samnites, Frentani, Marrucini, Marsi, Paeligni, Aequiculi, Vestini, and Sabini, bounded on the south by the Tifernus (Biferno), on the north probably by the Matrinus (Piomba) River, (5) Picenum, between the Aesis (Esino) and Matrinus rivers, (6) Umbria, including the ager Gallicus, bounded by the upper Tiber, Crustumius (Conca), and Aesis rivers, (7) Etruria, bounded by the Macra (Magra) and Tiber rivers, (8) Gallia Cispadana, limited by the Po River, from Placentia (Piacenza) to its mouth, and by the Crustumius, which was substituted for the Rubicon, (9) Liguria, bounded by the Varus (Var), Po, and Macra, (10) Venetia and Istria, including the Cenomani around Lake Garda in the west, and (11) Gallia Transpadana, bounded by the Alps, the Po River, and the Addua (Adda) River. This arrangement was retained almost unchanged until the emperor Diocletian’s reorganization (c. ad 290–300), when the diocese of Italy included the islands of Sicily, Corsica, and Sardinia, as well as Raetia and part of Pannonia to the north. In practice this diocese was divided into two areas, each under a vicarius: that of Italy with the four northern regions and that of Rome with the seven southern areas and the islands.