DIOCLETIAN (Gaius Aurelius Valerius Diocletianus)
- In November 284, Numerian was murdered in his litter, while being transported back to Rome, allegedly by his father-in-law, and praetorian commander, Lucius Flavius Aper. The murder went undetected until the smell of Numerian's decaying body, revealed the crime, at Nicomedia.
- Diocletian, commander of the bodyguard, was proclaimed emperor in place of Numerian, later conveniently doing away with Aper.
- In late summer 285, Carinus, Numerian's co-ruler in the west, met Diocletian in battle on the River Margus (Morava), near modern Belgrade. Carinus with the larger army was winning, but was killed by some of his officers who bore grudges against him for seducing their wives.
- Diocletian was born on 22nd December in 245 in Dalmatia, near Spalato (Split). He was of humble origins, and rose in the army, serving as commander in Moesia, on the middle Danube, and accompanying Carus on the Persian expedition of 283 as commander of the 'protectores domestici' or household cavalry.
- Two months into his reign, in November 285, he bestowed the title of Caesar (later Augustus)on one of his trusted fellow officers, Maximian, with control of the western provinces.
- Between 286 and 290, Diocletian campaigned on the Danube and on the eastern frontier.
- In 288 the two emperors mounted a combined operation against the Alemanni.
- Late in 286, Carausius, commander of the Roman North Sea fleet, seized control of Britain and pronounced himself emperor.
- On 1 March 293, Diocletian adopted Galerius Valerius Maximianus as son and Caesar, while Maximian did the same for his praetorian commander Julius Constantius. Diocletian as Augustus with Galerius as Caesar ruled the east, while Maximian as Augustus ruled the west with Constantius as Caesar. This system of four rulers was known as the Tetrarchy.
- Diocletian overhauled the tax system and endeavoured to halt inflation by issuing new coins of higher quality. When this measure failed, he issued an Edict of Maximum Prices which sought to fix the maximum prices at which goods and services could be bought and sold.
- In the east, Diocletian and Galerius persecuted Christians who refused to renounce their faith.
- Due to ill-health, Diocletian decided to retire. He persuaded Maximian to do the same and on 1 May 305, both abdicated. Constantius and Galerius became the new senior emperors, while Maximinus Daia and Severus were appointed Caesars in their place.
- Diocletian died at Split, on 3rd December 311.