The history of Rome is often divided into three basic phases: Monarchy, Republic, and Empire. However, historiographical terms have been introduced to detail more specific stages. For example, the Empire can be subdivided into Principate and Dominate. The Principate corresponds to the period from the rise to power of Augustus (27 BCE) to Diocletian (284 CE). The Dominate spans from Diocletian to the end of the Western Roman Empire in 476 CE or the end of the reign of Heraclius, the Eastern Emperor, in 641 CE, also known as the Late Empire.

Consequently, the Principate is equivalent to the Early Empire and is so named because the government was monarchical, even though the Senate was retained to maintain the illusion of a republic and avoid the perception of a return to monarchy. The ruler held the title of princeps, meaning “the first,” related to the most senior senator (princeps senatus) and the ancient idea advocated by the circle of Scipio Aemilianus of a primus inter pares.

In reality, it was only an illusion, as Augustus managed to accumulate offices and titles without seeming to do so on his own initiative. This allowed him to avoid accusations of dictatorship that had led to the death of his mentor, Julius Caesar. Later, his successors continued in this autocratic line, progressively reducing the powers of the Senate in practice. Thus, the princeps consolidated all powers (auctoritas, maiestas, and potestas) and effectively embodied a monarchy, no matter how collegial it may have seemed.

The enthronement of Vespasian brought a small change, as the princeps acquired a more distinct position compared to other state institutions. Since the ascent and retention of power depended on the military strength of the proclaimed general, potestas prevailed over auctoritas. In Roman law, the former referred to socially recognized power—the executive capacity to enforce the law—while the latter implied not only authority but also legitimation through merit.

With the Flavians and Antonines, the term imperator, referring to the military command received by generals (specifically consuls and praetors) during campaigns since republican times, began to gain ground.

At that time, imperium was a temporary authority that its holders had to relinquish at the end of their term, but it eventually also fell to the princeps. This trend continued with the Severans, but after them, Rome entered a turbulent period known as the Crisis of the Third Century, which further changed the landscape.

It began in 235 CE and ended in 284 CE, with a tumultuous succession of emperors incapable of establishing a new dynasty beyond their own rule and that of their sons—up to six emperors in the first year alone.

The solution came with the sixth, Diocletian, who also initiated a new phase in Roman historiographical periodization by starting the Dominate.

Diocletian, a lower-class Illyrian who rose through the military ranks until it propelled him to the throne, understood that the only way to prevent conflicts between rival candidates was to create a new system where governance was shared: the consortium imperii.

Thus, he established the tetrarchy, where four co-emperors (two augusti and two caesars) were each assigned a diocese or territory. There were six tetrarchies, although they were quite distorted because the system declined once its founder, the only true cohesive element, was absent.

Of interest here is that Diocletian undertook a practically comprehensive reconsideration of administration, including monetary reform, measures toward religious unity, and the creation of a large-scale civil bureaucracy—separate from the military to prevent temptations for governors and praetorian prefects—with numerous palace officials under the magister officiorum, whose appointment automatically meant entry into the Senate, to the detriment of the senatorial class.

He also changed the imperial title by officially adopting the dignity of dominus (lord or master) in place of princeps. Although the term had existed for a long time, it had not been used due to its negative connotations, as it was how slaves addressed their masters. Augustus discouraged its use, and Tiberius considered it an unworthy manifestation of servility, although the Severans began to associate the term with the throne.

In the 3rd century CE, the gradual transition from the Principate to the Dominate was not immediate but the result of a progressive transformation. Aurelian laid some foundations, and the same could be said of Gallienus and Trajan, during whose reigns the equites began their ascent. Similarly, after Diocletian, there were further reforms that strengthened the new era.

For instance, Constantine I embraced the idea of the supreme god but replaced the Sol Invictus with the Christian God, incorporating the chi-rho symbol and the labarum into imperial iconography. Later, the bishop of Rome was identified with the pontifex maximus, and Theodosius I, who also reigned alone for some years, established a church with a state structure.

By then, the capital had changed for strategic reasons, successively moving to Ulpia Serdica, Constantinople, and Ravenna. The old city was left with a prefectus urbi in charge.

In the Eastern Roman Empire, things became even more extreme, descending into autocratic absolutism and implementing extravagant palatine ceremonies. Justinian I was the last emperor to use the title dominus; from then on, basileus (king) was employed. The basileus was identified as an incarnation of the majesty of Rome, explaining why the crime of treason was termed lese-majesty.

Moreover, Diocletian’s tax system was based on land, obliging coloni (tenant farmers) to remain tied to it. Constantine reinforced this effect, restricting their movements and eventually causing them to become servi (serfs), narrowing or even equalizing their social status with that of slaves. This would later prove to be the beginning of the transition to the Middle Ages; the Herulian chieftain Odoacer took care of consummating it in 476 CE.

After all, as Goldsworthy notes, “the Late Empire was not conceived to be an efficient government but to keep the emperor in power.”

This article was first published on our Spanish Edition on November 22, 2023. Puedes leer la versión en español en Del Principado al Dominado, cuando los emperadores romanos se convirtieron en autócratas amantes del boato y la pompa


Sergei Ivanovich Kovaliov, Historia de Roma | A.D. Lee, From Rome to Byzantium AD 363 to 565: The Transformation of Ancient Rome | Christopher McKay, Ancient Rome: A Military and Political History | Pedro López Barja de Quiroga y Francisco Javier Lomas Salmonte, Historia de Roma | Michael Ivanovitc Rostovtzeff, Historia cosial y económica del Imperio Romano | Adrian Goldsworthy, La caída del Imperio romano. El ocaso de Occidente | F.W. Walbank, La pavorosa revolución. La decadencia del Imperio Romano de Occidente | VVAA, La transición del esclavismo al feudalismo | Wikipedia

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