Diocletian, Roman emperor from 284-305, was born Diocles - a Greek name - in the year 244 in Dalmatia, now the Balkans. Like so many others from the minor nobility he became a soldier - and at the age of 40 he was general of the 'Proctores Domestici', the cavalry unit belonging to the emperor's household.
When the ruling emperor, Carus, was struck by lightning during a campaign against the Persians his two sons Carinus & Numerian inherited the throne. Numerian "mysteriously" died on his way to Rome, and it totally had nothing to do with Diocles being responsible for his safety at all. I swear, total coincidence. He didn't even want to be emperor. But, you know, when the army insists it'd be rude to refuse...
The Battle agains Carinus
Carinus was of course not happy, and he gathered an army and marched against Rome and Diocletian, as he now styled himself. The battle stood at Margus in Moesia (now Serbia), and initially it looked like Carinus' larger and more experienced force would make short work of Diocletian's army. But as they were preparing to flee the unexpected happned; Carinus was killed by one of his bodyguards, as revenge for Carinus seducing his wife.
After this, Diocletian was hailed as emperor by the army which had nearly defeated him.
The Tetrarchy
As emperor, Diocletian was a great reformer. He had (correctly) identified that it was impossible for one man to hold together the vast Roman Empire, which was now both threatened on all fronts and by internal discord.
His solution was not new; he divided power between 2 senior emperors, each with an adopted junior emperor under him. From 286-305 he thus ruled alongside Maximian 'Herculius', with Galerius and Constantius I 'Chlorus' as junior emperors.
And then he abdicated, retired, and moved into a villa in Dalmatia to grow cabbages, a villa which nowadays forms the center of the city of Split in Croatia. Maximian also retired, in Campania south of Rome.
His Final Years
Diocletian is the only emperor of the third and fourth centuries who died a natural death, and he is the only emperor at all who voluntarily abdicated. And that is perhaps the greatest proof of how great a ruler he really was. After 50 years of chaos and civil war under 27 emperors, Diocletian ruled for 21 years before abdicating.
Sadly, his system, the Tetrarchy, collapsed almost immediately. The Roman Empire was again thrown into civil war - and Diocles died sick, tired and broken on December 3rd 311.
The End of Realistic Portraiture on Coins
With Diocletian the era where coins reflect what an emperor looked like in reality is definitely over. Due to hyperinflation, portrait quality had steadily declined as early as under Gallienus, and coins under Carus, Carinus, Numerian and Diocletian have virtually identical portraits. Not even after Diocletian's coinage reform - where this follis is from - are there any attempts to make the emperors look distinct.
In fact, realistic portraits are now a thing of the past for the next thousand years, after which the Renaissance kings begin to look to the rulers of antiquity as models - and to imitate their coins.
The Coin
This coins is a follis, a large coin measuring 28mm and weighing 10 grams. The reverse features the spirit of the Roman people - Genius Populi Romani. It was struck in Heraclea, now the small town of Marmara Ereğlisi in Turkey, about 90km west of Istanbul.
Obverse: IMP C C VAL DIOCLETIAN P F AVG, Laureate bust right
Reverse: GENIO POPVLI ROMANI, Genius standing left, holding patera and cornucopia
RIC VI 19a