On this date* in 284, one of Rome’s greatest emperors claimed the purple by summarily executing his rival before the approving army in Anatolia.

For half a century, the Roman Empire had waded through crisis. In its political manifestation, a parade of forgettable emperors had marched through the throne room, each to be assassinated, overthrown, or otherwise disposed of by some equally forgettable aspirant en route to a similarly unenviable end.

At length, out of this unpropitious bunch, rose one Diocles, a low-born Dalmatian of classical education whose martial gifts saw him rise through the legions. His opportunity came when the emperor Carus, barely a year on from succeeding his assassinated predecessor, died on campaign against Persia allegedly struck by lightning (quite possibly a euphemism for something more dagger-like), leaving his son Numerian in charge.

As the army meandered back to the friendly confines, Numerian secluded himself in his litter. And after a while, the litter started to stink.

Sometime on the journey, he’d been secretly killed — but by whom?

The principals this day are our leading suspects. (And it’s a little mystifying in either case just what was gained by leaving the body hidden so long.) We turn to Gibbon to narrate what must have been a riveting — not to mention definitive — proceeding adjudicating between them a few kilometers past Nicomedia (moder Izmit, Turkey) towards Chalcedon (now the Kadikoy district of Istanbul).

A general assembly of the army was appointed to be held at Chalcedon, whither Aper was transported in chains, as a prisoner and a criminal. A vacant tribunal was erected in the midst of the camp, and the generals and tribunes formed a great military council. They soon announced to the multitude that their choice had fallen on Diocletian, commander of the domestics or body-guards, as the person the most capable of revenging and succeeding their beloved emperor. The future fortunes of the candidate depended on the chance or conduct of the present hour. Conscious that the station which he had filled exposed him to some suspicions, Diocletian ascended the tribunal, and raising his eyes towards the Sun, made a solemn profession of his own innocence, in the presence of that all-seeing Deity. Then, assuming the tone of a sovereign and a judge, he commanded that Aper should be brought in chains to the foot of the tribunal. “This man,” said he, “is the murderer of Numerian;” and without giving him time to enter on a dangerous justification, drew his sword, and buried it in the breast of the unfortunate praefect.** A charge supported by such decisive proof was admitted without contradiction, and the legions, with repeated acclamations, acknowledged the justice and authority of the emperor Diocletian.

Though there isn’t any direct evidence of it, posterity is entitled to suspect on grounds of means, motive and opportunity, that the eventual beneficiary of Numerian’s demise — the emperor henceforth known as Diocletian — was its true author.

Whether obtained by fair means or foul, Diocletian put the laurels of state to good use, stabilizing government by introducing the “Tetrarchy” — the rule of the empire’s eastern and western halves by two emperors (“Augusti”) each aided by a “Caesar” who was also the heir apparent.

Diocletian’s two decades in power before his anomalous voluntary retirement constitute a watershed in the late history of Rome, and not only because the cycle of imperial assassinations and civil war took a welcome generation-long hiatus.

Although he’s also remembered for initiating the last major persecution of Christians, his administration set the stage for the rise of Constantine the Great, the Galilean’s first imperial champion. Constantine’s father was one of the original tetrarchs, the Caesar of the west.

And in the longer term, Diocletian’s division of the empire between east and west would sow the seed of the later separation of Byzantium and Rome, and the corresponding division in the Christian world. No surprise, then, that the first ruler profiled in Lars Brownworth’s 12 Byzantine Rulers podcast is this date’s executioner:

[audio:http://www.12byzantinerulers.com/audio/02-Diocletian.mp3]

More audiophilia about Diocletian and the tetrarchs in this lecture from Isabelle Pafford’s UC-Berkeley course on Roman history. (The first 6:45 or so consists of class business and carryover from previous lectures.)

[audio:http://webcast.berkeley.edu/media/s2008/hist106b/hist106b_20080425.mp3]

* As with much in the ancient world, sourcing is tenuous, and there is some scholarly debate over whether the events in this post should be ascribed to November 20, or to November 17, or to September 17, or to some other date. Since this blog, notwithstanding its title, embraces the occasional execution whose date is uncertain, I am prepared to wave aside textual uncertainty in the interest of a ripping good story.

** According to the Historia Augusta, Diocletian had a superstitious reason to carry out this bloodthirsty act personally.

This story my grandfather related to me, having heard it from Diocletian himself. “When Diocletian,” he said, “while still serving in a minor post, was stopping at a certain tavern in the land of the Tungri in Gaul, and was making up his daily reckoning with a woman, who was a Druidess, she said to him, ‘Diocletian, you are far too greedy and far too stingy,’ to which Diocletian replied, it is said, not in earnest, but only in jest, ‘I shall be generous enough when I become emperor.’ At this the Druidess said, so he related, ‘Do not jest, Diocletian, for you will become emperor when you have slain a Boar (Latin: Aper).’ ” … It is now well known and a common story that when he had killed Aper, the prefect of the guard, he declared, it is said, “At last I have killed my fated Boar.” My grandfather also used to say that Diocletian himself declared that he had no other reason for killing him with his own hand than to fulfill the Druidess’ prophecy and to ensure his own rule. For he would not have wished to become known for such cruelty, especially in the first few days of his power, if Fate had not impelled him to this brutal act of murder.

Part of the Themed Set: The “Ex” Stands For “Extrajudicial”.

On this day..

• 1663: Volkmar Limprecht
• 1928: William Charles Benson
• 2013: Joseph Paul Franklin, Larry Flynt's would-be assassin
• 1781: Margaret Tinkler, abortionist
• 1829: The slaves of the Greenup revolt
• 1936: Jose Antonio Primo de Rivera, Falange founder
• 1903: Peter Mortensen, divinely accused
• 2010: Mohsen bin Faisal Al Barik Al-Dossary, Saudi cop-killer
• 869 or 870: St. Edmund the Martyr
• 1903: Tom Horn
• 1676: Johan Johansson Griis, the Gävle Boy
• 1695: Zumbi dos Palmares