The Roman Emperor Augustus is named Pontifex Maximus, incorporating the position into that of the emperor.

The office of the Roman Emperor represented the pinnacle of power within the vast Roman Empire during its imperial period, a journey that officially began with the momentous granting of the title Augustus to Octavian in 27 BC. This marked a profound shift from the Roman Republic to an imperial system, fundamentally redefining Roman governance.

Throughout history, these powerful rulers adopted a rich tapestry of titles, each carrying specific implications and historical weight. While in English a Roman leader taking the reins as "emperor" often refers to his assumption of the esteemed Augustus title, later Eastern emperors would embrace basileus. Another frequently used title was Caesar, which became synonymous with heirs-apparent, signifying their designated path to imperial power. Imperator, initially a military honorific denoting a victorious commander, also became an integral part of the imperial nomenclature. Early emperors, ever mindful of republican sensibilities and eager to distance themselves from the concept of monarchy, carefully styled themselves as princeps civitatis, or 'first citizen.' They often shrewdly accumulated various republican titles, such as princeps senatus (leader of the Senate), consul, and, significantly, pontifex maximus, further blurring the lines between republican tradition and imperial authority.

The Emperor's Authority and Evolution of Rule

An emperor's legitimacy was a delicate balance, fundamentally resting on his command of the formidable Roman army and securing the crucial recognition of the Senate. Typically, an emperor might be proclaimed by his loyal troops on the battlefield, or formally invested with imperial titles by the Senate back in Rome, or in many cases, both. This interplay underscored the political complexities of imperial succession. While the earliest emperors initially reigned alone, the sheer scale and challenges of governing such a vast realm eventually led to the practice of co-emperors, who would sometimes divide the empire's administration between them, a precursor to later fundamental splits.

Crucially, the Romans maintained a distinct conceptual separation between their emperors and the idea of a king. The first emperor, Augustus, vehemently rejected any recognition as a monarch, understanding the deep-seated Roman aversion to kingship, a sentiment rooted in their expulsion of the Tarquin kings centuries prior. For approximately the first three hundred years of imperial rule, stretching from Augustus to the transformative reign of Diocletian, concerted efforts were made to portray emperors as leaders merely guiding the Republic, carefully avoiding any association with the despised kings of Rome that predated the Republic.

Diocletian and the Open Monarchy

This carefully maintained facade began to crumble with Diocletian, whose radical tetrarchic reforms irrevocably altered the nature of imperial power. These reforms not only divided the vast position into an emperor in the West and an emperor in the East but also ushered in an era where emperors ruled in an openly monarchic style. The nominal principle of a republic was largely abandoned. Yet, the distinction from "kings" persisted; while imperial succession often leaned towards heredity, it was never automatic. A suitable candidate, acceptable to both the army and the bureaucracy, was always a prerequisite, preventing the adoption of a purely hereditary system. Remarkably, even after the collapse of the Western Roman Empire, elements of the republican institutional framework—such as the Senate, consuls, and magistrates—were preserved, a testament to their enduring legacy.

The Shifting Capital and the Empire's Divide

A pivotal moment in Roman history was the reign of Constantine the Great. In 330 AD, he orchestrated the relocation of the imperial capital, the Caput Mundi (Head of the World), from Rome to a new city: Constantinople, previously known as Byzantium. This move had profound religious, political, and cultural implications, further solidifying the East's rising prominence.

The Western Roman Empire ultimately succumbed to immense pressures, collapsing in the late 5th century amidst repeated invasions of imperial territory by various Germanic barbarian tribes. Romulus Augustulus is frequently cited as the last emperor of the West, after his forced abdication in 476 AD. However, Julius Nepos maintained a claim to the title, recognized by the Eastern Empire, until his death in 480 AD. Following Nepos' demise, the Eastern emperor Zeno formally abolished the administrative division of the position, proclaiming himself the sole emperor of a notionally reunited Roman Empire.

The Enduring East: Byzantine Emperors

The subsequent Eastern emperors, ruling from Constantinople, steadfastly continued to style themselves "Emperor of the Romans" (later βασιλεύς Ῥωμαίων in Greek). In modern scholarship, however, they are often referred to as Byzantine emperors, a term used to differentiate this later, distinctly Hellenized phase of the Roman Empire. This Eastern continuation of Roman imperial tradition would last for nearly a millennium longer. The final chapter of this long lineage closed with Constantine XI Palaiologos, the last Roman emperor in Constantinople, who tragically died defending his city during the harrowing Fall of Constantinople to the Ottoman Empire in 1453.

From the reign of Heraclius in 629 AD onwards, the "Byzantine" emperors formally adopted the monarchic title of basileus (βασιλεύς), which became a title exclusively reserved for the Roman emperor and the ruler of the Sasanian Empire, while other rulers were demoted to the term rēgas.

Divine Authority and the Church

Beyond their political and military roles, some emperors were even accorded divine status after their death, reflecting the polytheistic nature of early Roman religion. With the eventual hegemony of Christianity across the empire, the emperor's role transformed. He came to be seen as God's chosen ruler on Earth, a special protector and leader of the Christian Church. However, this authority was not absolute; in practice, an emperor's influence on Church matters was frequently subject to challenge by powerful ecclesiastical figures.

The Legacy and Contested Claims

Due to the profound cultural rupture caused by the Turkish conquest, most Western historians generally consider Constantine XI as the last meaningful claimant to the title of Roman Emperor. Interestingly, from 1453, one of the titles adopted by the Ottoman Sultans was "Caesar of Rome" (Turkish: Kayser-i Rum), a claim they maintained as part of their imperial titulature until the Ottoman Empire itself dissolved in 1922. A separate Byzantine group of claimant Roman emperors existed in the Empire of Trebizond until its conquest by the Ottomans in 1461, though they had used a modified title since 1282.

The Medieval Problem of Two Emperors

For centuries, the Eastern emperors in Constantinople were recognized as legitimate Roman emperors not only within the lands they ruled but also by the papacy and the nascent Germanic kingdoms in the West. This widespread acceptance persisted until the deposition of Empress Irene of Athens in 797 AD. Objecting to a woman ruling the Roman Empire in her own right, and facing ongoing issues with the eastern clergy, the Papacy in Rome took a monumental step. They effectively created a rival lineage of Roman Emperors in Western Europe, crowning Charlemagne in 800 AD as the first of the Holy Roman Emperors. These emperors would rule the Holy Roman Empire for most of the period between 800 and 1806. Crucially, these Western emperors were never recognized as legitimate Roman emperors by the court in Constantinople, leading to a complex and often contentious "medieval problem of two emperors," each claiming the mantle of Rome.

The Pontifex Maximus: A Journey from Priest to Emperor

The office of pontifex maximus, Latin for "greatest priest," was a foundational and immensely important position within ancient Roman religion, serving as the chief high priest of the College of Pontiffs (Collegium Pontificum). Initially, this prestigious role was exclusively open to patricians, the Roman aristocracy, until 254 BC, when a plebeian finally broke this long-standing barrier and occupied the post. Despite being, in effect, the most powerful office within the Roman priesthood, the pontifex maximus was officially ranked fifth in the hierarchy of highest Roman priests (ordo sacerdotum), behind the rex sacrorum and the flamines maiores (Flamen Dialis, Flamen Martialis, Flamen Quirinalis).

What began as a distinctly religious office during the early Roman Republic gradually became politicized over time. This trend culminated in the Roman imperial period, starting with Augustus, when the position of pontifex maximus was subsumed into the office of the emperor. Subsequent emperors proudly bore the title pontifex maximus well into Late Antiquity, including figures like Gratian (r. 367–383). However, during Gratian's reign, a subtle but significant change occurred: the phrase was replaced in imperial titulature with the Latin phrase pontifex inclytus. This change, perhaps first adopted by the rebel Augustus Magnus Maximus (r. 383–388), was followed by Gratian's junior co-emperor Theodosius the Great and used by emperors thereafter, including co-augusti Valentinian III (r. 425–455) and Marcian (r. 450–457), and augustus Anastasius Dicorus (r. 491–518).

In a remarkable twist of historical continuity, the word pontifex and its derivative "pontiff" eventually became terms adopted for Christian bishops, including the Bishop of Rome. The title of pontifex maximus itself was subsequently applied to the Pope as the chief bishop of the Catholic Church. It can be found emblazoned on buildings, monuments, and coins of popes from the Renaissance and modern eras, a testament to its enduring legacy. The official list of titles for the Pope, as detailed in the Annuario Pontificio, includes "supreme pontiff" (Latin: summus pontifex) as the fourth title, with "bishop of Rome" holding the primary position.

FAQs About Roman Emperors and Their Titles

Who was the first Roman Emperor?
The first Roman Emperor was Augustus (born Octavian), who received the title in 27 BC, marking the official beginning of the Roman Imperial period.
What distinguished a Roman Emperor from a king?
Romans had a deep aversion to kingship, stemming from the expulsion of their early monarchs. Emperors, especially in the early centuries, were portrayed as "first citizens" (princeps civitatis) and leaders of the Republic, rather than absolute monarchs, though their power was immense.
What were some key titles used by Roman Emperors?
Prominent titles included Augustus, Caesar (often for heirs), Imperator (a military honorific), princeps civitatis ('first citizen'), and pontifex maximus (chief priest).
What was the significance of the pontifex maximus?
Originally the chief high priest of ancient Roman religion, the office of pontifex maximus gradually became politicized and was eventually absorbed into the position of the Roman Emperor, symbolizing the emperor's supreme religious authority. The title later influenced the Catholic Church's use of "pontiff" for bishops, including the Pope.
When did the Western Roman Empire fall?
The Western Roman Empire is generally considered to have fallen in 476 AD, with the forced abdication of Romulus Augustulus, following numerous invasions by Germanic tribes.
Who was the last Roman Emperor?
The last Roman Emperor in the East, and thus considered the last true successor to the Roman imperial tradition, was Constantine XI Palaiologos, who died during the Fall of Constantinople to the Ottoman Empire in 1453.
What was the "medieval problem of two emperors"?
This refers to the dispute that arose after the Papacy crowned Charlemagne as the first Holy Roman Emperor in 800 AD. The court in Constantinople, where the Eastern Roman (Byzantine) emperors ruled, did not recognize these Western emperors, leading to a complex rivalry over who legitimately held the title of Roman Emperor.