DIOCLETIAN'S TETRARCHIC SYSTEM OF GOVERNMENT
With emphasis on events relating to Roman Britain

Last updated: 19 October 2017

Diocletian the reforming Augustus

Diocletian - Caius Aurelius Verus Diocletianus - has come down in history as an astute politician, accomplished administrator and a stalwart leader. He assumed Imperium with Auctoritas as Augustus on 20 November 284, Diocletian determined to bring an end to the social and political chaos that had pervaded the Roman Empire for over fifty years by instituting several radical reforms. He was the driving force in reorganizing the Imperial Governmental System and reforming the coinage.

In 285 he appointed Marcus Aurelius Valerius Maximianus, a close friend and a renowned General like himself, as his Caesar elevating him to co-Augustus a year later. Diocletian subsequently divided the Empire geographically with himself as Augustus of the East and Maximian as Augustus of the West (thereby instituting a Dyarchy).

In 293 Diocletian finalized the Institution of a Tetrarchy -- government of the Empire by four interacting rulers -- two Augusti assisted by two subordinate Caesars, which each Augustus would personally select.

Although popular usage refers to this Institution as a singular Tetrarchy, in actuality there were three Tetrarchies composed of different Augusti and Caesars.

The First Tetrarchy

Diocletian emphasized his status as Senior Augustus by adopting Jovius as his Protector-God and assigning Herculius to Maximian. The two Caesars, chosen because of their proven leadership abilities, assisted the Augusti with civil administration and command of the armies. Caius Galerius Valerius Maximianus (Galerius Maximian) was chosen by Diocletian to be his Caesar of the East and Flavius Valerius Constantius (Constantius) was chosen by Maximian Herculius to be his Caesar of the West. Inasmuch as Constantius was instituted as Caesar at an earlier date than Galerius, he was designated senior in the Imperial hierarchy. The Empire was divided into four geographical areas of governance: Diocletian and Galerius Maximian maintained their eastern headquarters at Nicomedia and Thessalonica respectively, while Maximian Herculius and Constantius maintained their western headquarters at Milan and Trier respectively.

Abdication and Retirement of Diocletian and Maximian Herculius

It seems Diocletian had always envisioned that there would come a time when he (along with his co-Augustus?) would have to relinquish the reins of supreme power and retire (for whatever reason). He chose the occasion of his Vicennalia -- the twentieth anniversary of his assumption of power as Augustus and coincidentally the tenth anniversary (Decinnelia) of his institution of the Tetrarchy -- to Abdicate and retire and persuaded (compelled?) Maximian Herculius to do the same in concert with him. And so, in 303 the two Augusti announced their intention to simultaneously abdicate and retire (Maximian Herculius somewhat reluctantly) in 304, their titles and authority to be assumed by the Caesars, who in turn would appoint new Caesars thus perpetuating the system. This was, of course, the only instance of an Abdication during the Tetrarchy -- it didn't survive as an institution long enough to witness another one. Although Diocletian had provided a model for perpetuation of the system attending an Abdication, he didn't provide one to follow in the event of the sudden death of one, or both, of the reigning Augusti, and that had dire consequences for the Tetrarchy when Constantius (Augustus of the West) died suddenly in 306. Diocletian and Maximian Herculius did in fact jointly abdicate and retire in 305 to become Seniores Augusti.

The illness of Diocletian

Diocletian fell severely ill in 304 followed by a lengthy recovery. He emerged from this illness a much changed man mentally and physically. Members of his Court described him as being frail and sapped of the vigor and energy that had formerly characterized his every action and pursuit. He was never again the same man who had reformed the Roman governmental system and instituted the Tetrarchy.


Chronology of Events:

293 AD
* Diocletian institutes the Tetrarchy -- two Augusti assisted by two Caesars selected by them.
* Diocletian adopts Jovius (senior) as his Protector-God.
* Maximian adopts Herculius as his Protector-God.
* Galerius Maximian is selected by Diocletian to be his Caesar of the East.
* Constantius is selected by Maximian Herculius to be his Caesar of the West.

296 AD
* Constantius, Caesar of the West, invades Britain (April)
* Constantius defeats the Usurper Augustus, Allectus - restores Britain to the Empire.
* The official London Mint is established by Constantius

303 AD
* Diocletian and Maximian Herculius announce their intention to abdicate and retire.

304 AD
* Diocletian becomes severely ill followed by a lengthy recovery.

305 AD
* Joint abdication and retirement of Diocletian and Maximian Herculius on 1 May.

The Second Tetrarchy

In May of 305 Constantius succeeded Maximian Herculius as Augustus of the West and Galerius Maximian succeeded Diocletian as Augustus of the East, as planned. Flavius Valerius Severus (Severus), a close friend of Galerius Maximian, was appointed Caesar of the West by Constantius (as a result of persuasion by Galerius Maximian) and Galerius Valerius Maximinus Daia (Maximinus) was appointed Caesar of the East by Galerius Maximian (his uncle by marriage). The second Tetrarchy was thus created.

There has been a great deal of speculation on the part of historians as to why Constantius was influenced in this way by Galerius Maximian for they didn't have a particularly warm relationship. One theory holds that Constantius, unlike Galerius Maximian, was not much of a political mover and shaker -- i.e. he was more a warrior at heart and not much into court affairs and so he was indifferent to the appointment of Severus as his Caesar. This did present some problems for Constantius however. The familial affiliations of Severus were with Diocletian and Galerius Maximian which meant, like them, he was a Jovian and Constantius (along with his adoptive father, Maximian Herculius) was a Herculean. It was therefor necessary for Constantius to adopt him whereupon Severus assumed the name form Flavius Valerius Severus. Another thing that might have influenced Constantius's decison was the fact that his son, Constantine, was a "guest" in Galerius's court at the time and Constantius hoped to persuade Galerius Maximian to send Constantine to live with his father (which did in fact happen).

Constantius died at Eboracum (York) in Britain during a campaign against the warlike tribes of the North on 25 July 306. Before he died, Constantius conferred Imperium on his son, Flavius Valerius Constantinus (Constantine).


Chronology of Events:

305 AD
* Elevation of Constantius and Galerius Maximian to Augustus on 1 May.
* Severus is selected by Constantius to be his Caesar in the West.
* Maximinus is selected by Galerius Maximian to be his Caesar in the East.
* The second Tetrarchy is thus created.

306 AD
* Constantius becomes gravely ill during campaign against war-like tribes in northern Britain.
* Constantius confers Imperium on his son, Constantine.
* Constantius dies of natural causes at Eboracum (York), northern Britain on 25 July.

The Third Tetrarchy

Before he died in July of 306, Constantius had conferred Imperium on his son, Constantine. Although the army of Constantius wanted to proclaim Constantine Augustus, Galerius Maximian, the now de-facto senior Augustus, in the absence of any precedent or protocol to guide him, proclaimed Constantine Caesar of the West and elevated Severus to Augustus of the West (in accordance with the established rules for succession) thereby creating the Third Tetrarchy.

The Tetrarchic structure begins to crumble

On 28 October 306, the Citizens of Rome revolted against oppressive taxation and petitioned Marcus Aurelius Valerius Maxentius (Maxentius), son of retired Augustus Maximian Herculius, to assume Imperium. This he did, initially adopting the appellation of Princeps although his army proclaimed him Augustus. Maxentius persuaded his father, Maximian Herculius, to come out of retirement in order to serve as his "colleague Augustus". Galerius Maximian, the de-facto legitimate Augustus, rejected these actions as illegal and instructed Severus (because Rome was in his sphere of authority) to engage Maxentius and depose him.

Early in 307 Severus commanded an army that marched south into Italy to engage Maxentius as instructed by Galerius Maximian. Severus was not well served by this army that maintained loyalties to its previous commander, Maximian Herculius, and indeed many soldiers deserted Severus. The forces of Maxentius quickly defeated those of Severus who was captured and subsequently executed in Rome. Maximian Herculius thereupon set about organizing the defense of Rome against an anticipated attack by Galerius Maximian and in April travelled to Gaul seeking an alliance with Constantine, Caesar of the West, in order to strengthen his position. The alliance was duly consummated and cemented when Constantine married the daughter of Maximian Herculius, Fausta Flavia Maxima (Fausta). Constantine assumed the title and powers of Augustus later in the year (not recognized by Galerius Maximian) after affirmation by Maximian Herculius. There was now a legitmately appointed Augustus - Galerius Maximian, one dubiously assumptive Augustus - Maximian Herculius, and two very questionably appointed Augusti - Constantine and Maxentius. The structure of the Tetrarchy was now in shambles.


Chronology of Events:

306 AD
* Severus is proclaimed Augustus of the West by Galerius Maximian in July.
* Constantine is designated Caesar of the West by Galerius Maximian in July.
* On 25 July Constantine assumes control of the Western Mints -- Trier, Lyons & London.
* The Citizens of Rome revolt against oppressive taxation.
* The Citizens of Rome petition Maxentius (son of Maximian Herculius) to assume Imperium.
* Maxentius adopts the title of Princeps.
* Later the army at Rome proclaims Maxentius Augustus - rejected by Galerius Maximian.
* Maximian Herculius emerges from retirement to serve as "colleague Augustus" to Maxentius.
* Galerius Maximian instructs Severus to depose Maxentius.

307 AD
* Early in the year, Severus marches south into Italy with an army to engage Maxentius.
* The forces of Maxentius defeat those of Severus who is captured.
* Severus is subsequently executed in Rome.
* Maximian Herculius travels to Gaul seeking an alliance with Constantine.
* Constantine marries Fausta, daughter of Maximian Herculius, in April.
* Galerius Maximian marches into Italy with an army to depose Maxentius.
* Galerius Maximian is unsuccessful in subduing Maxentius and withdraws.
* Maxentius is left in control of much of Italy, Northern Africa and Spain.
* Constantine is affirmed as Augustus by Maximian Herculius.
* Constantine assumes the title and powers of Augustus sometime after 25 July.
* Galerius Maximian does not recognize Constantine's elevation to Augustus.


The inglorious demise of the Tetrarchy

In the spring of 308 Maximian Herculius had a falling out with his son, Maxentius, and left to join his now son-in-law, Constantine, in Gaul. In the autumn of 308 Galerius Maximian organized and convened a conference at Carnuntum consisting of himself, Diocletian and Maximian Herculius to discuss and resolve the "Augusti problem". Diocletian was but a shadow of his former self, both mentally and physically, due to the severe illness that befell him in 304 and consequently Galerius Maximian "ran the show" -- he was now the dominant force in the Tetrarchy. Galerius Maximian did not recognize either Constantine or Maxentius as Augustus, proposing instead that his old friend and comrade, Flavius Valerius Licinianus Licinius (Licinius) be appointed Augustus of the West to replace the deceased Severus and he obtained the concurrence of Diocletian and Maximian Herculius in this maneuver. Maxentius was declared an enemy of the state by the conferees and Maximian Herculius once more went into retirement. Galerius Maximian proposed that Constantine be recognized as Caesar, although Constantine did not acquiesce.

Constantine was incensed at his proposed "demotion" to Caesar subservient to Licinius as was Maximinus at the elevation of Licinius to Augustus, and so Galerius Maximian designated both of them Filius Augustorum: "son of the Augustus" -- a somewhat empty title of convenience and compromise -- in an attempt to mollify them.

There now followed a struggle between the Imperial Claimants: Maximian Herculius, who had again emerged from retirement as a self-proclaimed Augustus, and evidently with intentions to usurp Constantine, was defeated in battle by Constantine in 309 and committed suicide in 310. Maximinus was proclaimed Augustus by the troops of his army in the same year.

Galerius Maximian, the last surviving original Tetrarch and reigning senior Augustus, was afflicted with a fatal urinary/reproductive tract disease in 308 and died a painful, lingering, death on 5 May 311.

Maximinus and Maxentius formed a Military Compact early in 312 but Maxentius was defeated and killed by the forces of Constantine during a famous battle at Milvian bridge outside Rome later that year. The forces of Maximinus were defeated by those of Licinius in 313, Maximinus committing suicide later that year. Constantine and Licinius were subsequently proclaimed co-Augusti, bringing down the curtain on this Historical Period.


Chronology of Events:

308 AD
* Maximian Herculius quarrels with his son, Maxentius, early in the year.
* Maximian Herculius flees to Gaul to join his son-in-law, Constantine.
* Conference of Carnuntum: Galerius Maximian, Diocletian and Maximian Herculius.
* Galerius Maximian nominates Flavius Valerius Licinianus Licinius (Licinius), to be Augustus.
* Licinius is appointed Augustus of the West.
* Maximian Herculius goes into retirement yet again.
* Maxentius is declared to be an enemy of the State.

309 AD
* Constantine and Maximinus are appointed Filius Augustorum by Galerius Maximian.
* Maximian Herculius again emerges as a self-proclaimed Augustus.
* Maximian Herculius is defeated by Constantine in battle and deposed.

310 AD
* Maximian Herculius, accused of plotting against Constantine, commits suicide.
* Maximinus is proclaimed Augustus by the troops of his army.
* Galerius Maximian now recognizes Maximinus and Constantine as Augusti.

311 AD
* Galerius Maximian dies on 5 May after a long and painful illness.

312 AD
* Maximinus and Maxentius enter into a Military Compact.
* Maxentius is killed in battle with Constantine at Milvian bridge outside Rome on 28 October.

313 AD
* Licinius marries Constantia, (half) sister of Constantine in January.
* Maximinus is defeated in battle with Licinius and flees east.
* Maximinus subsequently commits suicide in Tarsus.
* Conference of Milan -- Constantine (West) and Licinius (East) are proclaimed co-Augusti.
* Edict of Milan -- proclaims religious tolerance of Christianity.


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