Roman Italy

 (the Latin and Italian name for the Italian Peninsula) was the homeland of the Romans and metropole of Rome's empire in classical antiquity. According to Roman mythology, Italy was the ancestral home promised by Jupiter to Aeneas of Troy and his descendants, 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 Celts in the North, the Etruscans and Umbrians in the Centre, and the Messapians (Illyrian Colonies) and Greeks 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 the local tribes and cities. 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. As provinces were being established throughout the Mediterranean, Italy maintained a special status which made it "not a province, but the (ruler) of the provinces". Such a status meant that Roman magistrates exercised the (police power) within Italy, rather than the (military power) used abroad. Italy's inhabitants had Latin Rights as well as religious and financial privileges.
The period between the end of the 2nd century BC and the 1st century BC was turbulent, beginning with the Servile Wars, continuing with the opposition of aristocratic élite to populist reformers and leading to a Social War in the middle of Italy. However, Roman citizenship was recognized to the rest of the Italics by the end of the conflict and then extended to Cisalpine Gaul when Julius Caesar became Roman Dictator. 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.
More than two centuries of stability followed, during which Italy was referred to as the (queen of the world) and (motherland of all lands). 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.
The crisis of the third century hit Italy particularly hard and left the eastern half of the Empire more prosperous. In 286 AD the Roman Emperor Diocletian moved the capital of the Western Roman Empire from Rome to Mediolanum. Nevertheless, the islands of Corsica, Sardinia, Sicily and Malta were added to Italy by Diocletian in 292 AD, and Italian cities such as Mediolanum and Ravenna continued to serve as capitals for the West.
The Bishop of Rome gained importance during Constantine's reign and was given religious primacy with the Edict of Thessalonica under Theodosius I. Italy was invaded several times by the barbarians and fell under the control of Odoacer, when Romulus Augustus was deposed in 476 AD. In the sixth century, except for about more than a decade between the end of the Gothic War in mid-550s and Lombard invasion of Italy in 568 when (Eastern) Roman Empire reunited Italy, Italy's territory was divided between the Eastern Roman Empire and the Germanic peoples. After that, Italy remained divided until 1861, when it was reunited by the House of Savoy in the Kingdom of Italy, which became the present-day Italian Republic in 1946.
Characteristics.
Following the end of the Social War in 88 BC, Rome had allowed its Italian allies full rights in Roman society and granted Roman citizenship to all the Italic peoples.
After having been for centuries the heart of the Roman Empire, from the 3rd century the government and the cultural center began to move eastward: first the Edict of Caracalla in 212 AD extended Roman citizenship to all free men within the imperial boundaries. Then, Christianity became the dominant religion during Constantine's reign (306–337), raising the power of other Eastern political centres. Although not founded as a capital city in 330, Constantinople grew in importance. It finally gained the rank of eastern capital when given an urban prefect in 359 and the senators who were "clari" became senators of the lowest rank as "clarissimi".
As a result, Italy began to decline in favour of the provinces, which resulted in the division of the Empire into two administrative units in 395: the Western Roman Empire, with its capital at Mediolanum (now Milan), and the Eastern Roman Empire, with its capital at Constantinople (now Istanbul). In 402, the capital was moved to Ravenna from Milan, confirming the decline of the city of Rome (which was sacked in 410 for the first time in seven centuries).
History.
The name "Italia" covered an area whose borders evolved over time. According to Strabo's "Geographica", before the expansion of the Roman Republic, the name was used by Greeks to indicate the land between the strait of Messina and the line connecting the gulf of Salerno and gulf of Taranto (corresponding roughly to the current region of Calabria); later the term was extended by Romans to include the Italian Peninsula up to the Rubicon, a river located between Northern and Central Italy.
In 49 BC, with the "Lex Roscia", Julius Caesar gave Roman citizenship to the people of the Cisalpine Gaul; while in 42 BC the hitherto existing province was abolished, thus extending Italy to the north up to the southern foot of the Alps.
Under Augustus, the peoples of today's Aosta Valley and of the western and northern Alps were subjugated (so the western border of Roman Italy was moved to the Varus river), and the Italian eastern border was brought to the Arsia in Istria. Lastly, in the late 3rd century, Italy came to also include the islands of Sicily, Corsica and Sardinia, as well as Raetia and part of Pannonia. The city of Emona (modern Ljubljana, Slovenia) was the easternmost town of Italy.
Augustan organization.
At the beginning of the Roman imperial era, Italy was a collection of territories with different political statuses. Some cities, called "municipia", had some independence from Rome, while others, the "coloniae", were founded by the Romans themselves. Around 7 BC, Augustus divided Italy into eleven "regiones", as reported by Pliny the Elder in his "Naturalis Historia":
Italy was privileged by Augustus and his heirs, with the construction, among other public structures, of a dense network of Roman roads. The Italian economy flourished: agriculture, handicraft and industry had a sensible growth, allowing the export of goods to the other provinces. The Italian population may have grown as well: three census were ordered by Augustus, to record the number of Roman citizens throughout the empire. The surviving totals were 4,063,000 in 28 BC, 4,233,000 in 8 BC, and 4,937,000 in AD 14, but it is still debated whether these counted all citizens, all adult male citizens, or citizens "sui iuris". 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.
Diocletianic and Constantinian re-organizations.
During the Crisis of the Third Century the Roman Empire nearly collapsed under the combined pressures of invasions, military anarchy and civil wars, and hyperinflation. In 284, emperor Diocletian restored political stability. He carried out thorough administrative reforms to maintain order. He created the so-called Tetrarchy whereby the empire was ruled by two senior emperors called Augusti and two junior vice-emperors called Caesars. He decreased the size of the Roman provinces by doubling their number to reduce the power of the provincial governors. He grouped the provinces into several dioceses (Latin: diocesis) and put them under the supervision of the imperial vicarius (vice, deputy), who was the head of the diocese. During the Crisis of the Third Century the importance of Rome declined because the city was far from the troubled frontiers. Diocletian and his colleagues usually resided in four imperial seats. The Augusti, Diocletian and Maximian, who were responsible for the East and West respectively, established themselves at Nicomedia, in north-western Anatolia (closer to the Persian frontier in the east) and Milan, in northern Italy (closer to the European frontiers) respectively. The seats of the Caesars were Augusta Treverorum (on the River Rhine frontier) for Constantius Chlorus and Sirmium (on the River Danube frontier) for Galerius who also resided at Thessaloniki.
Under Diocletian Italy became the Dioecesis Italiciana. It included Raetia. It was subdivided the following provinces:
Constantine subdivided the empire into four Praetorian prefectures. The "Diocesis Italiciana" became the Praetorian prefecture of Italy ("praefectura praetoria Italiae"), and was subdivided into two dioceses. It still included Raetia. The two dioceses and their provinces were:
Diocesis Italia annonaria (Italy of the annona - its inhabitants had to provide the administration in Milan and the troops stationed in that city the annona - food, wine and timber).
 Diocesis Italia Suburbicaria (Italy "under the government of the "urbs"", i.e. Rome)
Western Roman Empire.
In 330, Constantine inaugurated Constantinople. He established the imperial court, a Senate, financial and judicial administrations, as well as the military structures. The new city, however, did not receive an urban prefect until 359 which raised it to the status of eastern capital. After the death of Theodosius in 395 and the subsequent division of the empire Italy was part of the Western Roman Empire. As a result of Alaric's invasion in 402 the western seat was moved from Mediolanum to Ravenna. Alaric, king of Visigoths, sacked Rome itself in 410; something that hadn't happened for eight centuries. Northern Italy was attacked by Attila's Huns in 452. Rome was sacked in 455 again by the Vandals under the command of Genseric. 
According to "Notitia Dignitatum", one of the very few surviving documents of Roman government updated to the 420s, Roman Italy was governed by a praetorian prefect, "Prefectus praetorio Italiae" (who also governed the Diocese of Africa and the Diocese of Pannonia), one "vicarius", and one "comes rei militaris". 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 the fifth century, with the Emperors controlled by their barbarian generals, the Western imperial government maintained weak control over Italy, whose coasts were periodically under attack. 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. He was assassinated in 480 and may have been recognized by Odoacer. Italy remained under Odoacer and his Kingdom of Italy, and then under the Ostrogothic Kingdom. The Germanic successor states under Odoacer and Theodoric the Great continued to use the Roman administrative machinery, as well as being nominal subjects of the Eastern emperor at Constantinople. In 535 Roman Emperor Justinian invaded Italy which suffered twenty years of disastrous war. In August 554, Justinian issued a Pragmatic sanction which maintained most of the organization of Diocletian. The "Prefecture of Italy" thus survived, and came under Roman control in the course of Justinian's Gothic War.
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 - and footholds in the south Naples and the toe and heel of the peninsula.