It was ruled, not by emperors, but by annually elected magistrates (Roman Consuls above all) in conjunction with the senate. For various reasons, the 1st century BC was a time of political and military upheaval, which ultimately led to rule by emperors. The consuls' military power rested in the Roman legal concept of imperium, which literally means "command" (though typically in a military sense). Occasionally, successful consuls were given the honorary title imperator (commander), and this is the origin of the word emperor (and empire) since this title (among others) was always bestowed to the early emperors upon their accession.
The Augustus of Prima Porta
(early 1st century AD)
Rome suffered a long series of internal conflicts, conspiracies and civil wars from the late second century BC onwards, while greatly extending its power beyond Italy. Towards the end of this period, in 44 BC, Julius Caesar was briefly perpetual dictator before being assassinated. The faction of his assassins was driven from Rome and defeated at the Battle of Phillipi in 42 BC by an army led by Mark Antony and Caesar's adopted son Octavian. Antony and Octavian's division of the Roman world between themselves did not last and Octavian's forces defeated those of Antony and Cleopatra at the Battle of Actium in 31 BC.
In 27 BC the Senate and People of Rome made Octavian princeps ("first citizen") with proconsular imperium, thus beginning the Principate (the first epoch of Roman imperial history, usually dated from 27 BC to AD 284), and gave him the name "Augustus" ("the venerated"). Though the old constitutional machinery remained in place, Augustus came to predominate it. Although the republic stood in name, contemporaries of Augustus knew it was just a veil and that Augustus had all meaningful authority in Rome. Since his rule ended a century of civil wars, and began an unprecedented period of peace and prosperity, he was so loved that he came to hold the power of a monarch de facto if not de jure.
During the years of his rule, a new constitutional order emerged (in part organically and in part by design), so that, upon his death, this new constitutional order operated as before when Tiberius was accepted as the new emperor. The 200 years that began with Augustus's rule is traditionally regarded as the Pax Romana ("Roman Peace"). During this period, the cohesion of the empire was furthered by a degree of social stability and economic prosperity that Rome had never before experienced. Uprisings in the provinces were infrequent, but put down "mercilessly and swiftly" when they occurred. The sixty years of Jewish–Roman wars in the second half of the 1st century and the first half of the 2nd century were exceptional in their duration and violence.
The success of Augustus in establishing principles of dynastic succession was limited by his outliving a number of talented potential heirs: the Julio-Claudian dynasty lasted for four more emperors — Tiberius, Caligula, Claudius and Nero — before it yielded in 69 AD to the strife-torn Year of Four Emperors, from which Vespasian emerged as victor. Vespasian became the founder of the brief Flavian dynasty, to be followed by the Nerva–Antonine dynasty which produced the "Five Good Emperors": Nerva, Trajan, Hadrian, Antoninus Pius and the philosophically inclined Marcus Aurelius. In the view of the Greek historian Dio Cassius, a contemporary observer, the accession of the emperor Commodus in 180 AD marked the descent "from a kingdom of gold to one of rust and iron" a famous comment which has led some historians, notably Edward Gibbon, to take Commodus' reign as the beginning of the decline of the Roman Empire.
In 212, during the reign of Caracalla, Roman citizenship was granted to all freeborn inhabitants of the empire. But despite this gesture of universality, the Severan dynasty was tumultuous — an emperor's reign was ended routinely by his murder or execution — and, following its collapse, the Roman Empire was engulfed by the Crisis of the Third Century, a period of invasions, civil strife, economic disorder, and plague. In defining historical epochs, this crisis is sometimes viewed as marking the transition from Classical Antiquity to Late Antiquity.
Aurelian (reigned 270–275) brought the empire back from the brink and stabilized it. Diocletian completed the work of fully restoring the empire, but declined the role of princeps and became the first emperor to be addressed regularly as domine, "master" or "lord". This marked the end of the Principate, and the beginning of the Dominate. Diocletian's reign also brought the empire's most concerted effort against the perceived threat of Christianity, the "Great Persecution". The state of absolute monarchy that began with Diocletian endured until the fall of the Eastern Roman Empire in 1453.
A 5th-century papyrus showing a parallel Latin-Greek text of a speech by Cicero
Diocletian divided the empire into four regions, each ruled by a separate emperor (the Tetrarchy). Confident that he fixed the disorders that were plaguing Rome, he abdicated along with his co-emperor, and the Tetrarchy soon collapsed. Order was eventually restored by Constantine, who became the first emperor to convert to Christianity, and who established Constantinople as the new capital of the eastern empire. During the decades of the Constantinian and Valentinian dynasties, the empire was divided along an east–west axis, with dual power centers in Constantinople and Rome. The reign of Julian, who attempted to restore Classical Roman and Hellenistic religion, only briefly interrupted the succession of Christian emperors. Theodosius I, the last emperor to rule over both East and West, died in 395 AD after making Christianity the official religion of the empire.
The Western Roman Empire began to disintegrate in the early 5th century as Germanic migrations and invasions overwhelmed the capacity of the Empire to assimilate the migrants and fight off the invaders. The Romans were successful in fighting off all invaders, most famously Attila the Hun,[citation needed] though the empire had assimilated so many Germanic peoples of dubious loyalty to Rome that the empire started to dismember itself. Most chronologies place the end of the Western Roman Empire in 476, when Romulus Augustulus was forced to abdicate to the Germanic warlord Odoacer. By placing himself under the rule of the Eastern Emperor, rather than naming himself E\emperor (as other Germanic chiefs had done after deposing past emperors), Odoacer ended the Western Empire by ending the line of Western emperors.
The empire in the East — often known as the Byzantine Empire, but referred to in its time as the Roman Empire or by various other names — had a different fate. It survived for almost a millennium after the fall of its Western counterpart and became the most stable Christian realm during the Middle Ages. During the 6th century, Justinian briefly reconquered Northern Africa and Italy, but Roman possessions in the West were reduced to southern Italy and Sicily within a few years after Justinian's death. In the east, partially resulting from the destructive Plague of Justinian, the Romans were threatened by the rise of Islam, whose followers rapidly conquered the territories of Syria, Armenia and Egypt during the Byzantine-Arab Wars, and soon presented a direct threat to Constantinople. In the following century, the Arabs also captured southern Italy and Sicily. Slavic populations were also able to penetrate deep into the Balkans.
The Romans, however, managed to stop further Islamic expansion into their lands during the 8th century and, beginning in the 9th century, reclaimed parts of the conquered lands. In 1000 AD, the Eastern Empire was at its height: Basileios II reconquered Bulgaria and Armenia, culture and trade flourished. However, soon after the expansion was abruptly stopped in 1071 with their defeat in the Battle of Manzikert. The aftermath of this important battle sent the empire into a protracted period of decline. Two decades of internal strife and Turkic invasions ultimately paved the way for Emperor Alexius I Comnenus to send a call for help to the Western European kingdoms in 1095.
The West responded with the Crusades, eventually resulting in the Sack of Constantinople by participants in the Fourth Crusade. The conquest of Constantinople in 1204 fragmented what remained of the Empire into successor states, the ultimate victor being that of Nicaea. After the recapture of Constantinople by Imperial forces, the Empire was little more than a Greek state confined to the Aegean coast. The Roman Empire finally collapsed when Mehmed II conquered Constantinople on 29 May 1453.
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