The Roman Empire at its greatest extent controlled approximately 6.5 million square kilometres (2.5 million square miles) of land surface.
Traditional stories handed down by the ancient Romans themselves explain the earliest history of their city in terms of legend and myth. The most familiar of these myths, and perhaps the most famous of all Roman myths, is the story of Romulus and Remus, the twins who were suckled by a she-wolf. They decided to build a city, but after an argument, Romulus killed his brother and the city took his name. According to the Roman annalists, this happened on 21 April 753 BC. This legend had to be reconciled with a dual tradition, set earlier in time, that had the Trojan refugee Aeneas escape to Italy and found the line of Romans through his son Iulus, the namesake of the Julio-Claudian dynasty. This was accomplished by the Roman poet Virgil in the first century BC.
After the legendary foundation by Romulus, Rome was ruled for a period of 244 years by a monarchical system, initially with sovereigns of Latin and Sabine origin, later by Etruscan kings. The tradition handed down seven kings: Romulus, Numa Pompilius, Tullus Hostilius, Ancus Marcius, Tarquinius Priscus, Servius Tullius and Tarquinius Superbus.
In 509 BC the Romans expelled the last king from their city and established an oligarchic republic. Rome then began a period characterized by internal struggles between patricians (aristocrats) and plebeians (small landowners), and by constant warfare against the populations of central Italy: Etruscans, Latins, Volsci, Aequi, Marsi. After becoming master of Latium, Rome led several wars (against the Gauls, Osci-Samnites and the Greek colony of Taranto, allied with Pyrrhus, king of Epirus) whose result was the conquest of the Italian peninsula, from the central area up to Magna Graecia.
The third and second century BC saw the establishment of Roman hegemony over the Mediterranean and the East, through the three Punic Wars (264–146 BC) fought against the city of Carthage and the three Macedonian Wars (212–168 BC) against Macedonia.Then were established the first Roman provinces: Sicily, Sardinia and Corsica, Hispania, Macedonia, Greece (Achaia) and Africa.
15th-century miniature depicting the Sack of Rome (410)
From the beginning of the 2nd century BC, power was contested between two groups of aristocrats: the optimates, representing the conservative part of the Senate, and the populares, which relied on the help of the plebs (urban lower class) to gain power. In the same period, the bankruptcy of the small farmers and the establishment of large slave estates provoked the migration to the city of a large number of people. The continuous warfare made necessary a professional army, which was more loyal to its generals than to the republic. Due to that, in the second half of the second century and during the first century BC there were conflicts both abroad and internally: after the failed attempt of social reform of the populares Tiberius and Gaius Gracchus, and the war against Jugurtha, there was a first civil war between Gaius Marius and Sulla. To this followed a major slave revolt under Spartacus, and then the establishment of the first Triumvirate with Caesar, Pompey and Crassus.
The conquest of Gaul made Caesar immensely powerful and popular, which lead to a second civil war against the Senate and Pompey. After his victory, Caesar established himself as dictator for life. His assassination led to a second Triumvirate among Octavian (Caesar's grandnephew and heir), Mark Antony and Lepidus, and to another civil war between Octavian and Antony. The former in 27 BC became princeps civitatis and got the title of Augustus, founding the principate, a diarchy between the princeps and the senate.
Rome was established as a de facto empire, which reached its greatest expansion in the second century under the Emperor Trajan, Rome was confirmed as caput Mundi, i.e. the capital of the world, an expression which had already been given in the Republican period. During its first two centuries, the empire saw as rulers, emperors of the Julio-Claudian, Flavian (who also built eponymous amphitheater, known as the Colosseum) and Antonine dynasties. This time was also characterized by the spread of the Christian religion, preached by Jesus Christ in Judea in the first half of the first century (under Tiberius) and popularized by his apostles through the empire and beyond. The Antonine age is considered the apogee of the Empire, whose territory ranged from the Atlantic Ocean to the Euphrates and from Britain to Egypt.
In the third century, at the end of the Antonine dynasty, with the Severan dynasty the principatus was substituted by a military government, which was soon followed by a destabilising period of military anarchy known as the Crisis of the Third Century. At the same time the economy deteriorated, inflation rose and the historical enemies of Rome, the Germanic tribes in the West and the Persian Empire in the East, continued to bear pressure on the frontiers.
Crowning of Charlemagne in Old Saint Peter's Basilica, on 25 December 800
Emperor Diocletian (284) attempted to alleviate the economic and military problems by introducing the dominate (an absolute monarchy where the emperor was deified), imposing price controls and decentralising the administration: the emperor divided the empire into twelve dioceses, ruling under the title of Augustus the eastern half (with residence in Nicomedia) and naming Maximian Augustus of the western half, whose capital was moved to Mediolanum. The succession was regulated with the creation of the Tetrarchy: each Augustus, in fact, had to appoint a junior emperor, named Caesar, who would rule part of the roman territory on behalf of his Augustus and who would become, at the end, the new emperor.
After the abdication of Diocletian and Maximian in 305 and many dynastic conflicts, this system collapsed, and the new ruler, Constantine, centralized power again and, with the Edict of Milan in 313, gave freedom of worship for Christians, pledging himself to give stability to the new religion. He built several churches, gave the civil power of Rome to Pope Sylvester I and founded in the eastern part a new capital city; Constantinople.
Christianity became the official religion of the empire, thanks to an edict issued in 380 by Theodosius, who was the last emperor of a unified empire: after his death, in fact, his sons, Arcadius and Honorius, divided the empire into a western and an eastern part. The capital of the western Roman Empire became Ravenna.
Rome, which had lost its central role in the administration of the empire, was sacked in 410 by the Visigoths led by Alaric I, but also embellished by the construction of sacred buildings by the popes (with the collaboration of the emperors). The city, impoverished and depopulated, suffered a new looting in 455, by Genseric, king of the Vandals. The weak emperors of the fifth century could not stop the decay, until the deposition of Romulus Augustus on 22 August 476 marked the end of the Western Roman Empire and, for many historians, the beginning of the Middle Ages.
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