Roman emperor
The Roman emperor was the ruler and monarchical head of state of the Roman Empire, starting with the granting of the title Augustus to Octavian in 27 BC. The title of imperator, originally a military honorific, was usually used alongside Caesar, originally a cognomen. When a given Roman is described as becoming emperor in English, it generally reflects his accession as augustus, and later as. Early emperors also used the title princeps alongside other Republican titles, notably Roman consul and pontifex maximus.
The legitimacy of an emperor's rule depended on his control of the Roman army and recognition by the Senate; an emperor would normally be proclaimed by his troops, or by the Senate, or both. The first emperors reigned alone; later emperors would sometimes rule with co-emperors to secure the succession or to divide the administration of the empire between them. The office of emperor was thought to be distinct from that of a Rex . Augustus, the first emperor, resolutely refused recognition as a monarch. For the first three hundred years of Roman emperors, efforts were made to portray the emperors as leaders of the Republic, fearing any association with the kings who ruled Rome prior to the Republic.
From Diocletian, whose reformed tetrarchy divided the position into one emperor in the West and one in the East, emperors ruled in an openly monarchic style. Although succession was generally hereditary, it was only hereditary if there was a suitable candidate acceptable to the army and the bureaucracy, so the principle of automatic inheritance was not adopted, which often led to several claimants to the throne. Despite this, elements of the republican institutional framework were preserved even after the end of the Western Empire.
Constantine the Great, the first Christian emperor, moved the capital from Rome to Constantinople, formerly known as Byzantium, in 330 AD. Roman emperors had always held high religious offices, early emperors were even worshiped as gods, at least following their death when they were said to have become divine. Under Constantine there arose the specifically Christian idea that the emperor was God's chosen ruler on earth, a special protector and leader of the Christian Church, a position later termed Caesaropapism. In practice, an emperor's authority on Church matters was frequently subject to challenge. In the later period, although theoretically one empire, there were two emperors, one in the east and one in the west. The Western Roman Empire collapsed in the late 5th century after multiple invasions by Germanic barbarian tribes, with no recognized claimant to Emperor of the West remaining after the death of Julius Nepos in 480. Instead, the Eastern emperor Zeno proclaimed himself as the sole emperor of a theoretically undivided Roman Empire. The subsequent Eastern emperors ruling from Constantinople styled themselves as " of the Romans" but are often referred to in modern scholarship as Byzantine emperors.
The papacy and Christianised Germanic kingdoms of the West acknowledged the Eastern emperors until the accession of Empress Irene in 797. After this, the papacy created a rival lineage of Roman emperors in western Europe, the Holy Roman Emperors, which ruled the Holy Roman Empire for most of the period between 800 and 1806. These emperors were never recognized in Constantinople and their coronations resulted in the medieval problem of two emperors. The last Eastern emperor was Constantine XI Palaiologos, who died during the Fall of Constantinople to the Ottoman Empire in 1453. After conquering the city, Ottoman sultans adopted the title "Caesar of the Romans". A Byzantine group of claimant emperors existed in the Empire of Trebizond until its conquest by the Ottomans in 1461, although they had used a modified title since 1282.
Background and beginning
Modern historians regard Augustus as the first emperor, whereas Julius Caesar is considered the last dictator of the Roman Republic, a view that is shared by the Roman writers Plutarch, Tacitus, and Cassius Dio. Conversely, the majority of Roman writers, including Pliny the Younger, Suetonius and Appian, as well as most of the ordinary people of the Empire, thought of Julius Caesar as the first emperor. Caesar did indeed rule the Roman state as an autocrat, but he failed to create a stable system to maintain himself in power. His rise to power was the result of a long and gradual decline in which the Republic fell under the influence of powerful generals such as Gaius Marius and Sulla.At the end of the Republic no new or singular title indicated the individual who held supreme power. Insofar as emperor could be seen as the English translation of the Latin imperator, then Julius Caesar had been an emperor, like several Roman generals before him. Instead, by the end of the Caesar's civil wars, it became clear that there was certainly no consensus to return to the old-style monarchy, but that the period when several officials would fight one another had come to an end.
Julius Caesar, and then Augustus after him, accumulated offices and titles of the highest importance in the Republic, making the power attached to those offices permanent, and preventing anyone with similar aspirations from accumulating or maintaining power for themselves. Julius Caesar had been pontifex maximus since 64 BC; held the offices of consul and dictator five times since 59 BC, and was appointed dictator in perpetuity in 44 BC, shortly before his assassination. He had also become the de facto sole ruler of Rome in 48 BC, when he defeated his last opposition at the Battle of Pharsalus. His killers proclaimed themselves as the liberatores and the restorers of the Republic, but their rule was cut short by Caesar's supporters, who almost immediately established a new dictatorship.
File:Kameo Augustus mit Tritonengespann KHM IXa 56.jpg|thumb|left|Cameo of Augustus in a quadriga drawn by tritons at the Kunsthistorisches Museum, Vienna
In his will, Caesar appointed his grandnephew Octavian as his heir and adopted son. He inherited his property and lineage, the loyalty of most of his allies, and – again through a formal process of senatorial consent – an increasing number of the titles and offices that had accrued to Caesar. In August 43 BC, following the death of both consuls of the year, Octavian marched to Rome and forced the Senate to elect him consul. He then formed the Second Triumvirate alongside Mark Antony and Lepidus, dividing the Roman world among them. Lepidus was sidelined in 36 BC, and relations between Octavian and Antony soon deteriorated. In September 31 BC, Octavian's victory at Actium put an end to any effective opposition and confirmed his supremacy over Rome.
In January 27 BC, Octavian and the Senate concluded the so-called "First settlement". Until then Octavian had been ruling the state with his powers as triumvir, even though the Triumvirate itself disappeared years earlier. He announced that he would return the power to the Senate and People of Rome, but this was only an act. The Senate confirmed Octavian as princeps, the "first among equals", and gave him control over almost all Roman provinces for a tenure of ten years. This limitation was only superficial, as he could renew his powers indefinitely. In addition, the Senate awarded him the appellation of augustus. The honorific itself held no legal meaning, but it denoted that Octavian now approached divinity, and its adoption by his successors made it the de facto main title of the emperor. He also received the civic crown alongside several other insignias in his honor. Augustus now held supreme and indisputable power, and even though he still received subsequent grants of powers, such as the granting of tribunicia potestas in 23 BC, these were only ratifications of the powers he already possessed.
Most modern historians use 27 BC as the start date of the Roman Empire. This is mostly a symbolic date, as the Republic had essentially disappeared many years earlier. Ancient writers often ignore the legal implications of Augustus' reforms and simply write that he "ruled" Rome following the murder of Caesar, or that he "ruled alone" after the death of Mark Antony. Most Romans thus simply saw the "emperor" as the individual that ruled the state, with no specific title or office attached to him.
Augustus actively prepared his adopted son Tiberius to be his successor and pleaded his case to the Senate for inheritance on merit. After Augustus' death in AD 14, the Senate confirmed Tiberius as princeps and proclaimed him as the new augustus. Tiberius had already received imperium maius and tribunicia potestas in AD 4, becoming legally equal to Augustus but still subordinate to him in practice. The "imperial office" was thus not truly defined until the accession of Caligula, when all of Tiberius' powers were automatically transferred to him as a single, abstract position that was symbolized by his sacred title of augustus.
Powers under the Principate
The legal authority of the emperor derived from an extraordinary concentration of individual powers and offices that were extant in the Republic and developed under Augustus and later rulers, rather than from a new political office. Under the Republic, these powers would have been split between several people, who would each exercise them with the assistance of a colleague and for a specific period of time. Augustus held them all at once by himself, and with no time limits; even those that nominally had time limits were automatically renewed whenever they lapsed. The Republican offices endured and emperors were regularly elected to the most prominent of them: the consulship and censorship. This early period of the Empire is known as the "Principate", derived from the title princeps used by the early emperors.The most important bases of the emperor's power were his supreme power of command and tribunician power as personal qualities, separate from his public office. Originally, the powers of command where divided in consular imperium for Rome and proconsular imperium for the provinces. This division became obsolete in 19 BC when Augustus was given consular imperium – despite leaving the consulship in 23 BC – and thus control over all troops. This overwhelming power was referred to as imperium maius to indicate its superiority to other holders of imperium, such as the proconsuls of the few senatorial provinces and allies such as Agrippa. The governors appointed to the imperial provinces only answered to the emperor himself, who could maintain or replace them at will.
File:Silver Denarius of Augustus.jpg|thumb|205x205px|left|Denarius of Augustus.
The tribunician power, first assumed by Augustus in 23 BC, gave him authority over the tribune of the plebs without having to actually hold the office – a tribune was by definition a plebeian, whereas Augustus, although born into a plebeian family, had become a patrician when he was adopted into the gens Julia. By adopting the role of a tribune, Augustus was presenting himself as the representative of the common man and the protector of democracy. As always, this was not a sudden grant of power; Augustus had been receiving several powers related to the tribunes, such as sacrosanctity, since 36 BC. With this powers, he could veto any act or proposal of any magistrate, propose laws and convoke the Senate. His sacrosanctity also made him untouchable, and any offence against him could be treated as a crime of treason. The tribunician power was arguably the most stable and important of the emperor's powers. Despite being a perpetual title, it was always renewed each year, which often coincided with the beginning of a new regnal year.
The office of censor was not fully absorbed into the imperial office until the reign of Domitian, who declared himself "perpetual censor" in AD 85. Before this, the title had been only used by Claudius, Vespasian and Titus.
The emperor also had power over religious affairs, which led to the creation of a worship cult. Augustus became pontifex maximus in 12 BC, after the death of the former triumvir Lepidus. Emperors from the reign of Gratian onward used the style pontifex inclytus. The title of pontifex maximus was eventually adopted by the bishops of Rome during the Renaissance. The last known emperors to use the title were Valentinian III and Marcian, in the 5th century.
The only surviving document to directly refer to the emperor's power is the Lex de imperio Vespasiani, written shortly after Vespasian's formal accession in December 69. The text, of which only the second part survives, states that Vespasian is allowed to: make treaties; hold sessions and propose motions to the Senate; hold extraordinary sessions with legislative power; endorse candidates in elections; expand the pomerium; and use discretionary power whenever necessary. The text further states that he is "not bound by laws", and that any previous act was retroactively considered legitimate. There is no mention of imperium nor tribunicia potestas, although these powers were probably given in the earlier clauses. There is also no mention of any "imperial office", and the title of "emperor" is never used. The imperial titles are treated as inseparable of the person, which is reflected in the name Imperator Caesar Vespasianus Augustus. This Lex sometimes related to the Lex regia mentioned in the Corpus Juris Civilis of Eastern emperor Justinian I, who cites the early 3rd-century writer Ulpian. This was probably a later construct, as its very name, which derives from rex, would have been utterly rejected in the West. The Eastern Greek-speaking half of the Empire had always regarded the emperors as open monarchs, and called them as such.