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 basileus. Early emperors also used the title princeps ("first one") alongside other Republican titles, notably 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 ("king"). 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 (Senate, consuls, and magistrates) 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; 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. 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 (although in practice he had no authority in the West). The subsequent Eastern emperors ruling from Constantinople styled themselves as "Basileus of the Romans" (Ancient Greek: βασιλεύς Ῥωμαίων, Basileus Romaíon) but are often referred to in modern scholarship as Byzantine emperors.

The papacy and 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" (kayser-i Rûm). 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.

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 ("liberators") and the restorers of the Republic, but their rule was cut short by Caesar's supporters, who almost immediately established a new dictatorship.