Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilisation, characterised by an autocratic form of government, headed by an Emperor, and large territorial holdings around the Mediterranean Sea in Europe, Africa, the Middle East and Asia Minor. The 500 year old republic which preceded it had been severely destabilised through a series of civil wars and political infighting in the Senate. Several events marked the transition of power from the Roman Senate to an autocratic Emperor. Julius Caesar's appointment as perpetual dictator in 44 BC after his victory over Pompey resulted in his assassination, triggering a power vacuum that led to a succession of conflicts between supporters of Caesar and the Senate. Octavian, Caesar's adopted son, defeated Mark Antony and Cleopatra at the Battle of Actium in 31 BC after inheriting Caesar's estates. Following Antony and Cleopatra's suicides and the annexation of the Ptolemaic Empire in 30 BC, the Roman Senate granted the honorific title Augustus to Octavian three years later in 27 BC, effectively bringing about the end of the Roman Republic.

The imperial successor to the Republic endured for some 500 years. Following Octavian's victory, the size of the Empire was dramatically increased, conquering Dalmatia, Pannonia, Noricum, expanding into Germania and Africa as well as completing the conquest of Hispania. The first two centuries of the Empire's existence were a period of unprecedented political stability and prosperity known as the Pax Romana, or "Roman Peace". Following the assassination of the mad Emperor Caligula in 41, the Praetorian Guard briefly considered returning power to the Roman Senate, however their proclamation of Claudius ensured the Empire's longevity. Under Claudius, the Empire underwent its first major expansion since Augustus, annexing Thrace, Noricum, Pamphylia, Lycia, Judea, Mauretania and the elusive island of Britannia. After Claudius' successor, Nero, committed suicide in 68, the Empire suffered a period of brief civil wars, as well as a concurrent major rebellion in Judea, during which four different legionary generals were proclaimed Emperor. Vespasian emerged triumphant in 69 after the Battle of Bedriacum, establishing the Flavian dynasty. The rule of the Five Good Emperors in the late 1st and 2nd centuries saw widespread territorial and social expansion. The Empire reached its greatest extent under Trajan, the second in this line, conquering Nabataea, Dacia, Armenia and Mesopotamia.

The reign of Commodus began a period of decline in imperial prosperity. Commodus' assassination in 192 triggered the Year of the Five Emperors, of which Septimus Severus emerged victorious the following year after the Battle of Issus. The assassination of Alexander Severus in 235 led to the Crisis of the Third Century in which 26 men were declared Emperor by the Roman Senate over a fifty year period. The Empire split into three competing factions; the Gallic Empire, the Palmyrene Empire and the Roman Empire proper, suffering through foreign invasions and economic depression. Aurelian re-conquered the Gallic and Palmyrene factions at the battles of Chalons and Emesa respectively, reuniting the Empire proper, earning him the title Restitutor Orbis or "Restorer of the World". However, it was not until the reign of Diocletian that the Empire was successfully stabilised with the introduction of the Tetrarchy. Under Diocletian's reign, the empire was divided in half, with the Western half centred on Mediolanum administered by Maximian, while the Eastern half was administered from Nicomedia by Diocletian himself.

The division was ultimately unsuccessful, leading to a civil war that was finally ended by Constantine I, who defeated his rivals Maxentius and Licinius, winning the decisive engagement at the Milivian bridge, becoming sole ruler of east and west. Constantine subsequently shifted the capital of the east from Nicomedia to Byzantium, which was renamed Constantinople in his honour. It remained the capital of the east until its demise in 1453. Constantine also adopted Christianity which later became the official state religion of the Empire, ending centuries of Roman polytheism and leading to a massive rise in power of the Christian religion. From Constantine's death in 337, the dominion of the Empire was gradually eroded by abuses of power, civil wars, barbarian migrations and invasions, military reforms and economic depression, triggered by the catastrophic defeat of the Emperor Valens at the Battle of Adrianople in 378. The Sack of Rome in 410 by the Visigoths and again in 455 by the Vandals greatly accelerated the Western Empire's decay, while the deposition of the Emperor Romulus Augustus in 476 by Odoacer is generally accepted to mark the collapse of central government in the west. The Eastern Roman Empire, centred in Constantinople, endured for another thousand years, eventually falling to the Ottoman Turks under Mehmed II in 1453.

During its tenure, the Roman Empire was the most powerful economic, cultural, political and military force in the known world. It was the largest empire of the Classical antiquity period, and the eighteenth^{[citation needed]} largest empire in world history. At its height under Trajan, it covered 6.8 million square kilometres and held sway over some 70 million people, at that time, 21% of the world's entire population. The longevity and vast extent of the Empire ensured the lasting influence of Latin and Greek language, culture, religion, inventions, architecture, philosophy, law and forms of government on the Empire's descendants. Throughout the European medieval period, attempts were even made to establish successors to the Roman Empire, including the Crusader state, the Empire of Romania and the Holy Roman Empire. By means of European expansionism, especially through the Spanish, French, Portuguese and British empires, Roman and Greek culture was spread on a worldwide scale, playing a significant role in the development of the modern world.

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