The Roman Empire is the name given to both the domain obtained by the city-state of Rome (Italy) and also the corresponding phase of that civilization, characterized by an autocratic form of government. It succeeded the 500 year-old Roman Republic (510 BC – 1st century BC), which had been weakened by the conflict between Gaius Marius and Sulla and the civil war of Julius Caesar against Pompey. Several dates are commonly proposed to mark the transition from Republic to Empire, including the date of Julius Caesar's appointment as perpetual dictator (44 BC), the victory of Caesar's heir Octavian at the Battle of Actium (September 2, 31 BC), and the Roman Senate's granting to Octavian the honorific Augustus (January 16, 27 BC)

The Latin term Imperium Romanum ("Roman Empire"), probably the best-known Latin expression where the word "imperium" denotes a territory, indicates the part of the world under Roman rule. From the time of Augustus to the Fall of the Western Empire, Rome dominated Western Eurasia, comprising the majority of its population. Roman expansion began long before the state was changed into an Empire and reached its zenith under emperor Trajan with the conquest of Dacia in AD 116. During this territorial peak the Roman Empire controlled approximately 5 900 000 km² (2,300,000 sq.mi.) of land surface.

Rome's influence upon the culture, law, technology, arts, language, religion, government, military, and architecture of Western civilization continues to this day.

Attempting to secure the borders of the empire upon the rivers Danube and Elbe, Octavian ordered the invasions of Illyria, Moesia, and Pannonia (south of the Danube), and Germania (west of the Elbe).
At first everything went as planned, but then disaster struck. The Illyrian tribes revolted and had to be crushed, and three full legions under the command of Publius Quinctilius Varus were ambushed and destroyed at the Battle of the Teutoburg Forest in AD 9 by German barbarians under the leadership of Arminius. Being cautious, Augustus secured all territories west of Rhine and contented himself with retaliatory raids. The rivers Rhine and Danube became the permanent borders of the Roman empire in the North.

Augustus had three grandsons by his daughter Julia. None of the three lived long enough to succeed him. He therefore was succeeded by his stepson Tiberius, the son of his wife Livia from her first marriage. At the time of Tiberius' death most of the people who might have succeeded him had been brutally murdered. The logical successor (and Tiberius' own choice) was his grandnephew, Germanicus' son Gaius (better known as Caligula or "little boots").

Caligula started out well, by putting an end to the persecutions and burning his uncle's records. Unfortunately, he quickly lapsed into illness. The Caligula that emerged in late 37 demonstrated features of mental instability that led modern commentators to diagnose him with such illnesses.

Claudius had long been considered a weakling and a fool by the rest of his family. He was, however, neither paranoid like his uncle Tiberius, nor insane like his nephew Caligula, and was therefore able to administer the empire with reasonable ability. He improved the bureaucracy and streamlined the citizenship and senatorial rolls. He also proceeded with the conquest and colonization of Britain (in 43) and incorporated more Eastern provinces into the empire. He ordered the construction of a winter port for Rome, at Ostia, thereby providing a place for grain from other parts of the Empire to be brought in inclement weather.

The death of Claudius paved the way for Agrippina's own son, the 17-year-old Lucius Domitius Nero.

Nero left the rule of Rome to his mother and his tutors, particularly Lucius Annaeus Seneca. However, as he grew older, his paranoia and desire for power increased and he had his mother and tutors executed. During Nero's reign, there were a series of major riots and rebellions throughout the Empire: in Britannia, Armenia, Parthia, and Iudaea. Nero's inability to manage the rebellions and his basic incompetence became evident quickly and, in 68, even the Imperial guard renounced him.

The main enemy in the West were, arguably, the "barbarian tribes" behind the Rhine and the Danube. Augustus had tried to conquer them, but ultimately failed and these "barbarians" were greatly feared. But by and large they were left in peace, in order to fight amongst themselves, and were simply too divided to pose a serious threat.

The forced suicide of emperor Nero, in 68, was followed by a brief period of civil war (the first Roman civil war since Antony's death in 31 BC) known as the year of the four emperors.

Between June of 68 and December of 69, Rome witnessed the successive rise and fall of Galba, Otho and Vitellius until the final accession of Vespasian, first ruler of the Flavian dynasty. This period of civil war has become emblematic of the cyclic political disturbances in the history of the Roman Empire. The military and political anarchy created by this civil war had serious implications, such as the outbreak of the Batavian rebellion.

Nerva went to set a new tone: he released those imprisoned for treason, banned future prosecutions for treason, restored much confiscated property, and involved the Roman Senate in his rule. Trajan marched first on Armenia. He deposed the king and annexed it to the Roman Empire. Then he turned south into Parthia itself, taking the cities of Babylon, Seleucia and finally the capital of Ctesiphon in 116. He continued southward to the Persian Gulf, whence he declared Mesopotamia a new province of the empire and lamented that he was too old to follow in the steps of Alexander the Great.

Hadrian's reign was marked by a general lack of major military conflicts. He surrendered Trajan's conquests in Mesopotamia, considering them to be indefensible. There was almost a war with Parthia around 121, but the threat was averted when Hadrian succeeded in negotiating a peace. Hadrian's army crushed a massive Jewish uprising in Judea (132–135).
In Britain, he ordered the construction of a wall, the famous Hadrian's Wall as well as various other such defenses in Germany and Northern Africa. His domestic policy was one of relative peace and prosperity.

Pius' reign was comparatively peaceful; there were several military disturbances throughout the Empire in his time, in Mauretania, Iudaea, and amongst the Brigantes in Britain, but none of them are considered serious.

Germanic tribes and other peoples launched many raids along the long north European border, particularly into Gaul and across the Danube — Germans, in turn, may have been under attack from more warlike tribes farther east. His campaigns against them are commemorated on the Column of Marcus Aurelius. In Asia, a revitalized Parthian Empire renewed its assault. The Pax Romana, or "Roman Peace", ended with the reign of Commodus.

The Severan dynasty includes the increasingly troubled reigns of Septimius Severus (193–211), Caracalla (211–217), Macrinus (217–218), Elagabalus (218–222), and Alexander Severus (222–235). Hereafter, the crisis of the Third Century (235-284) started followed by the gradual transition through The Tetrarchs from a single united empire to the later divided Western and Eastern empires.

For the following two years conflicts continued. Valens personally led a campaign against them in 378. Gratian provided his uncle with reinforcements from the Western Roman army. However this campaign proved disastrous for the Romans. The two armies approached each other near Adrianople. Valens was apparently overconfident of his numerical superiority of his own forces over the Goths. Some of his officers advised caution and to await to arrival of Gratian, others urged for an immediate attack and eventually prevailed over Valens, eager to have all of the glory for himself rushed into battle.

On August 9, 378, the Battle of Adrianople resulted in the crushing defeat of the Romans and the death of Valens. Contemporary historian Ammianus Marcellinus estimated that two thirds of the Roman army were lost in the battle. The last third managed to retreat. The battle had far reaching consequences. Veteran soldiers and valuable administrators were among the heavy casualties. There were few available replacements at the time, leaving the Empire with problems of finding suitable leadership. The Roman army would also start facing recruiting problems. In the following century much of the Roman army would consist of Germanic mercenaries.

Gratian governed the Western Roman Empire with energy and success for some years, but he gradually sank into indolence. He is considered to have become a figurehead while Frankish general Merobaudes and bishop Ambrose of Milan jointly acted as the power behind the throne. Gratian lost favor with factions of the Roman Senate by prohibiting traditional paganism at Rome and relinquishing his title of Pontifex Maximus. The senior Augustus also became unpopular to his own Roman troops because of his close association with so-called barbarians. He reportedly recruited Alans to his personal service and adopted the guise of a Scythian warrior for public appearances.

Meanwhile Gratian, Valentinian II and Theodosius were joined by a fourth Augustus. Theodosius proclaimed his oldest son Arcadius to be an Augustus in January, 383 in an obvious attempt to secure succession. The boy was only still five or six years old and held no actual authority. Nevertheless he was recognized as a co-ruler by all three Augusti. The increasing unpopularity of Gratian would cause the four Augusti problems later that same year. Spanish Celt general Magnus Maximus, stationed in Roman Britain, was proclaimed Augustus by his troops in 383 and rebelling against Gratian he invaded Gaul. Gratian fled from Lutetia (Paris) to Lugdunum (Lyon), where he was assassinated on August 25, 383 at the age of twenty-five.

Maximus was a firm believer of the Nicene Creed and introduced state persecution on charges of heresy, which brought him in conflict with Pope Siricius who argued that the Augustus had no authority over church matters. But he was an Emperor with popular support and his reputation survived in Romano-British tradition and gained him a place in the Mabinogion, compiled about a thousand years after his death. Following Gratian's death, Maximus had to deal with Valentinian II, actually only 12 years old, as the senior Augustus. The first few years the Alps would serve as the borders between the respective territories of the two rival Western Roman Emperors. Maximus controlled Britain, Gaul, Hispania and Africa. He chose Augusta Treverorum (Trier) as his capital.

Maximus soon entered negotiations with Valentinian II and Theodosius, attempting to gain their official recognition. By 384, negotiations were unfruitful and Maximus tried to press the matter by settling succession as only a legitimate Emperor could do: proclaiming his own infant son Flavius Victor an Augustus. The end of the year found the Empire having five Augusti (Valentinian II, Theodosius I, Arcadius, Magnus Maximus and Flavius Victor) with relations between them yet to be determined. Theodosius was left a widower, in 385, following the sudden death of Aelia Flaccilla, his Augusta. He was remarried to the sister of Valentinean II, Galla, and the marriage secured closer relations between the two legitimate Augusti.

In 386 Maximus and Victor finally received official recognition by Theodosius but not by Valentinian. In 387, Maximus apparently decided to rid himself of his Italian rival. He crossed the Alps into the valley of the Po and threatened Milan. Valentinian and his mother fled to Thessaloniki from where they sought the support of Theodosius. Theodosius indeed campaigned west in 388 and was victorious against Maximus. Maximus himself was captured and executed in Aquileia on July 28, 388. Magister militum Arbogastes was sent to Trier with orders to also kill Flavius Victor. Theodosius restored Valentinian to power and through his influence had him converted to Orthodox Catholicism. Theodosius continued supporting Valentinian and protecting him from a variety of usurpations.

In 392 Valentinian was murdered in Vienne. Theodosius succeeded him, ruling the entire Roman Empire. Theodosius had two sons and a daughter, Pulcheria, from his first wife, Aelia Flacilla. His daughter and wife died in 385. By his second wife, Galla, he had a daughter, Galla Placidia, the mother of Valentinian III, who would be Emperor of the West.
Theodosius was the last Emperor who ruled over the whole Empire. After his death in 395 he gave the two halves of the Empire to his two sons Arcadius and Honorius; Arcadius became ruler in the East, with his capital in Constantinople, and Honorius became ruler in the west, with his capital in Milan and later Ravenna.

Though the Roman state would continue to have two emperors, the Eastern Romans considered themselves Roman in full. Latin was used in official writings as much as, if not more than, Greek. The two halves were nominally, culturally and historically, if not politically, the same state.

Fall of the Western Roman Empire (395–476)

The year 476 is generally accepted as the end of the Western Roman Empire. That year, Orestes refused the request of Germanic mercenaries in his service for lands in Italy. The dissatisfied mercenaries, including the Heruli, revolted. The revolt was led by the Germanic chieftain Odoacer. Odoacer and his men captured and executed Orestes. Within weeks, Ravenna was captured and Romulus Augustus was deposed, the event that has been traditionally considered the fall of the Roman Empire, at least in the West.

Odoacer then sent the Imperial Regalia back to the emperor Zeno, and the Roman Senate informed Zeno that he was now the Emperor of the whole empire. Zeno soon received two deputations. One was from Odoacer requesting that his control of Italy be formally recognized by the Empire, in which he would acknowledge Zeno's supremacy. The other deputation was from Nepos, asking for support to regain the throne. Zeno granted Odoacer the title Patrician.

Zeno told Odoacer and the Roman Senate to take Nepos back. However, Nepos never returned from Dalmatia, even though Odoacer issued coins in his name. Upon Nepos' death in 480, Zeno claimed Dalmatia for the East; J. B. Bury considers this the real end of the Western Roman Empire. Odoacer attacked Dalmatia, and the ensuing war ended with Theodoric the Great, King of the Ostrogoths, conquering Italy under Zeno's authority.

In essence, the "fall" of the Roman Empire to a contemporary depended a great deal on where they were and their status in the world. On the great villas of the Italian Campagna, the seasons rolled on without a hitch. The local overseer may have been representing an Ostrogoth, then a Lombard duke, then a Christian bishop, but the rhythm of life and the horizons of the imagined world remained the same. Even in the decayed cities of Italy consuls were still elected. In Auvergne, at Clermont, the Gallo-Roman poet and diplomat Sidonius Apollinaris, bishop of Clermont, realized that the local "fall of Rome" came in 475, with the fall of the city to the Visigoth Euric. In the north of Gaul, a Roman kingdom existed for some years and the Franks had their links to the Roman administration and military as well.

As the west would decline during the 5th century, the richer east would be spared much of the destruction, and in the 6th century the Eastern Empire under the emperor Justinian I reconquered the Italian peninsula from the Ostrogoths, North Africa from the Vandals (their kingdom collapsing in 533), southern Spain, and a narrow tract of the Illyrian coast. These gains were lost during subsequent reigns. Of the many accepted dates for the end of the Roman state, the latest is 610. This is when the Emperor Heraclius made sweeping reforms, forever changing the face of the empire. Greek was readopted as the language of government and Latin influence waned. By 610, the Classical Roman Empire had fallen into the rule of the Greeks and evolved into what modern historians now call the Middle Age Byzantine Empire, although the Empire was never called that way by its contemporaries (rather it was called Romania or Basileia Romaion). The Byzantine Greeks continued to call themselves Romans until their fall to Ottoman Turks in 1453. That year the Roman Empire was ultimately ended by the Fall of Constantinople. Constantine XI, emperor of the Byzantine Empire during 1453 is considered the last Roman emperor. The Greek ethnic self-descriptive name "Romans" survives to this day.

Legacy

Several states claiming to be the Roman Empire's successor arose after the fall of the Western Empire. First it was the Byzantine Empire, its direct political heir. Then the Holy Roman Empire, an attempt to resurrect the Empire in the West, was established in 800 when Pope Leo III crowned Charlemagne as Roman Emperor on Christmas Day, though the empire and the imperial office did not become formalized for some decades. After the fall of Constantinople, the Russian Tsardom, as inheritor of the Byzantine Empire's Orthodox Christian tradition, counted itself as the third Rome (with Constantinople being the second). And when the Ottomans, who based their state around the Byzantine model, took Constantinople in 1453, Mehmed II established his capital there and claimed to sit on the throne of the Roman Empire, and he even went so far as to launch an invasion of Italy with the purpose of "re-uniting the Empire", although Papal and Neapolitan armies stopped his march on Rome at Otranto in 1480. Constantinople was not officially renamed to Istanbul until March 28, 1930.

But excluding these states claiming their heritage, the Roman state lasted (in some form) from the founding of Rome in 753 BC to the fall in 1461 of the Empire of Trebizond (a successor state and fragment of the Byzantine Empire which escaped conquest by the Ottomans in 1453), for a total of 2214 years. The Roman impact on Western and Eastern civilizations lives on. In time most of the Roman achievements have been duplicated by later civilizations. For example, the technology for cement was rediscovered 1755–1759 by John Smeaton.

The Empire contributed many things to the world, such as the (more-or-less) modern calendar, the institutions of Christianity and aspects of modern neo-classicistic architecture. The extensive system of roads, which were constructed by the Roman Army, still last to this day. Because of this network of roads, the amount of time necessary to travel between destinations in Europe did not decrease until the 19th century after the invention of steam power.

The Roman Empire also contributed its form of government, which influences various constitutions including those of most European countries, and that of the United States, whose framers remarked, in creating the Presidency, that they wanted to inaugurate an "Augustan Age." The modern world also inherited legal thinking from the Roman law, codified in Late Antiquity. Governing a vast territory, the Romans developed the science of public administration to an extent never before conceived nor necessary, creating an extensive civil service and formalized methods of tax collection. The western world today derives its intellectual history from the Greeks, but it derives its methods of living, ruling and governing from those of the Romans.