According to Roman mythology, Italy was the ancestral home promised by Jupiter to Aeneas of Troy and his descendants, Romulus and Remus, who were the founders of Rome.

Aside from the legendary accounts, Rome was an Italic city-state that changed its form of government from Kingdom to Republic and then grew within the context of a peninsula dominated by the Gauls, Ligures, Veneti, Camunni and Histri in the North, the Etruscans, Latins, Falisci, Picentes, Umbri, Sabines in the Centre, and the Iapygian tribes (such as the Messapians), the Oscan tribes (such as the Samnites), and Greek colonies in the South.

The consolidation of Italy into a single entity occurred during the Roman expansion in the peninsula, when Rome formed a permanent association with most of other the local tribes and cities.

[3][page needed] The strength of the Italian confederacy was a crucial factor in the rise of Rome, starting with the Punic and Macedonian wars between the 3rd and 2nd century BC.

In the context of the transition from Republic to Principate, Italy swore allegiance to Octavian Augustus and was then organized in eleven regions from the Alps to the Ionian Sea with more than two centuries of stability afterward.

Several emperors made notable accomplishments in this period: Claudius incorporated Britain into the Roman Empire, Vespasian subjugated the Great Revolt of Judea and reformed the financial system, Trajan conquered Dacia and defeated Parthia, and Marcus Aurelius epitomized the ideal of the philosopher king.

With the development of provincial governments and the proliferation of citizenship, Italy gradually lost its position as the empire's heartland, though it retained the ideological value as Roman homeland.

The Bishop of Rome had gained importance gradually from the reign of Constantine, and was given religious primacy with the Edict of Thessalonica under Theodosius I. Italy was invaded several times by the wandering Germanic peoples and fell under the control of Odoacer, when Romulus Augustus was deposed in 476 AD.

Christianity then began to establish itself as the dominant religion from Constantine's reign (306–337), raising the power of Eastern metropolises, later grouped into Pentarchy.

[18] Estimates for the population of mainland Italy, including Cisalpine Gaul, at the beginning of the 1st century range from 6,000,000 according to Karl Julius Beloch in 1886, to 14,000,000 according to Elio Lo Cascio in 2009.

[19] During the Crisis of the Third Century, the Roman Empire was on the verge of disintegration under the combined pressures of invasions, military anarchy, civil wars, and hyperinflation.

The regions of Italy were governed at the end of the fourth century by eight consulares (Venetiae et Histriae, Aemiliae, Liguriae, Flaminiae et Piceni annonarii, Tusciae et Umbriae, Piceni suburbicarii, Campaniae, and Siciliae), two correctores (Apuliae et Calabriae and Lucaniae et Bruttiorum) and seven praesides (Alpium Cottiarum, Rhaetia Prima and Secunda, Samnii, Valeriae, Sardiniae, and Corsicae).

In 476, with the abdication of Romulus Augustulus, the Western Roman Empire had formally fallen unless one considers Julius Nepos, the legitimate emperor recognized by Constantinople as the last.

The Germanic successor states under Odoacer and Theodoric the Great continued to use the Roman administrative apparatus, as well as being nominal subjects of the Eastern emperor at Constantinople.

As a result of the Lombard invasion in 568, the Byzantines lost most of Italy, except the territories of the Exarchate of Ravenna – a corridor from Venice to Lazio via Perugia – and footholds in the south Naples and the toe and heel of the peninsula.