* 286 – Emperor Diocletian elevates his general Maximian to co-emperor with the rank of Augustus and gives him control over the Western regions of the Roman Empire.

Ar., lxiv, and De Syn., xviii ), St Athanasius does not recall from memory being a first hand witness to the onset of the great persecution by the Tetrarchy of Diocletian and Maximian in February 303, for in referring to the events of this period he makes no direct appeal to his own personal recollections, but falls back on tradition.

At some time in 285 at Mediolanum ( Milan, Italy ), Diocletian raised his fellow-officer Maximian to the office of Caesar, making him co-emperor.

Some historians state that Diocletian, like some emperors before him, adopted Maximian as his filius Augusti, his " Augustan son ", upon his appointment to the throne.

The relationship between Diocletian and Maximian was quickly couched in religious terms.

Circa 287 Diocletian assumed the title Iovius, and Maximian assumed the title Herculius.

The titles were probably meant to convey certain characteristics of their associated leaders ; Diocletian, in Jovian style, would take on the dominating roles of planning and commanding ; Maximian, in Herculian mode, would act as Jupiter's heroic subordinate.

Religious legitimization elevated Diocletian and Maximian above potential rivals in a way military power and dynastic claims could not.

Carausius fled the Continent, proclaimed himself Augustus, and spurred Britain and northwestern Gaul into open revolt against Maximian and Diocletian.

It has even been suggested that Maximian usurped the title, and was only later recognized by Diocletian in hopes of avoiding civil war.

This suggestion is unpopular, as it is clear that Diocletian meant for Maximian to act with a certain amount of independence.

The following spring, as Maximian prepared a fleet for an expedition against Carausius, Diocletian returned from the East to meet Maximian.

Diocletian invaded Germania through Raetia while Maximian progressed from Mainz.

Diocletian met Maximian in Milan in the winter of 290 – 91, either in late December 290 or January 291.

Some time after his return, and before 293, Diocletian transferred command of the war against Carausius from Maximian to Flavius Constantius.

They were joined by blood and marriage ; Diocletian and Maximian now styled themselves as brothers.

Their homes were distant from political life, but Diocletian and Maximian were close enough to remain in regular contact with each other.

Diocletian and Maximian were both present on 11 November 308, to see Galerius appoint Licinius to be Augustus in place of Severus, who had died at the hands of Maxentius.

* 285 – Diocletian appoints Maximian as Caesar, co-ruler.

* 285 – Diocletian appoints Maximian as Caesar and co-ruler.

The point of the work is to describe the deaths of the persecutors of Christians: Nero, Domitian, Decius, Valerian, Aurelian, and the contemporaries of Lactantius himself, Diocletian, Maximian, Galerius, and Maximinus.

* 293 – Roman Emperors Diocletian and Maximian appoint Constantius Chlorus as Caesar to Maximian.

* 305 – Diocletian and Maximian retire from the office of Roman Emperor.

After Diocletian stepped down on 1 May 305, his successors began to struggle for control of the Roman Empire almost immediately.

Diocletian moved into Egypt to suppress him, first putting down rebels in the Thebaid in the autumn of 297, then moving on to besiege Alexandria.

According to Lactantius, he came armed with plans to reconstitute the Tetrarchy, force Diocletian to step down, and fill the Imperial office with men compliant to his will.

On his way through Pannonia he put down the usurper Sabinus Iulianus, and encountered the army of Diocletian in Moesia.

From this time forward down to the latest period of the empire, for nearly a thousand years, the name occurs more or less frequently in the Fasti, and it was borne by the emperors Maximinus, Maximianus, Maxentius, Diocletian, Constantius, Constantine the Great and others.

In the early 4th century, Diocletian personally put down a rebellious governor and immediately afterward, transferred the Legio III Augusta from Lambaesis to another, unknown base within the region.

Diocletian convinces Maximian to step down.

Diocletian tried to solve this problem by re-establishing an adoptive succession with a senior ( Augustus ) and junior ( Caesar ) emperor in each half of the Empire, but this system of Tetrarchy broke down within one generation ; the hereditary principle was re-established with generally unfortunate results, and civil war was thereafter the main method of establishing new imperial regimes.

Friedrich Münter believes he can trace the letter down to the time of Diocletian ; but this is not generally accepted.

Diocletian delegated further on 1 March 293, appointing Galerius and Constantius as Caesars, junior co-emperors.

In 308 the Emperor emeritus Diocletian chaired a historic meeting with his co-emperors Maximian and Galerius in Carnuntum to solve the rising tensions within the tetrarchy.

In that year the co-emperors of the late Roman Empire resolved once again on an attempt to eradicate Christianity, the senior emperor, Diocletian, relying this time on the services of a subordinate emperor, Maximian.

Administrative division of the sprawling Empire into a Western and Eastern half with co-emperors for each began under Diocletian in 285 and was periodically abolished and recreated for the next two centuries until final abolishment by the Byzantine emperor Zeno in 480.

* Tetrarchs, the four co-emperors of the Roman Empire instituted by the Emperor Diocletian

The name originated in the equation of the two co-emperors Diocletian and Maximian with the Roman gods Jove and Hercules.

Diocletian set up 12 dioceses ( later several were split ; see under Roman province ), originally two to four for each of the four co-emperors under the short-lived Tetrarchy ( two senior Augusti, each above a Caesar ), each governed by a Vicarius who substituted for or acted on behalf of the praetorian prefect.

At the conclusion of the Persian wars in 299, co-emperors Diocletian and Galerius traveled from Persia to Syrian Antioch ( Antakya ).

The table counted the years starting from the presumed birth of Christ, rather than the accession of the emperor Diocletian on 20 November 284, or as stated by Dionysius: " sed magis elegimus ab incarnatione Domini nostri Jesu Christi annorum tempora praenotare ..." It is assumed Dionysius Exiguus intended either 1 AD or 1 BC to be the year of Christ's birth ( a " year zero " does not exist in this calendar ).

Art dating from the Diocletian period ( 286 – 305 AD ) in Villa Romana del Casale, Sicily depicts women in garments resembling bikinis in mosaics on the floor.

After the deaths of Carus and his son Numerian on campaign in Persia, Diocletian was proclaimed Emperor.

Weakened by illness, Diocletian left the imperial office on 1 May 305, and became the only Roman emperor to voluntarily abdicate the position.

There is a contemporary issue of coins suggestive of an imperial adventus ( arrival ) for the city, but some modern historians state that Diocletian avoided the city, and that he did so on principle, as the city and its Senate were no longer politically relevant to the affairs of the Empire and needed to be taught as much.

If Diocletian ever did enter Rome shortly after his accession, he did not stay long ; he is attested back in the Balkans by 2 November 285, on campaign against the Sarmatians.

At the conclusion of discussions with the Persians, Diocletian re-organized the Mesopotamian frontier and fortified the city of Circesium ( Buseire, Syria ) on the Euphrates.

Afterwards, during 299 and 302, as Diocletian was then residing in the East, it was Galerius ' turn to campaign victoriously on the Danube.

By the end of his reign, Diocletian had secured the entire length of the Danube, provided it with forts, bridgeheads, highways, and walled towns, and sent fifteen or more legions to patrol the region ; an inscription at Sexaginta Prista on the Lower Danube extolled restored tranquilitas at the region.

Rhetorically Eusebius records the Oracle as saying " The just on Earth ..." These impious, Diocletian was informed by members of the court, could only refer to the Christians of the Empire.

When Diocletian reappeared in public on 1 March 305, he was emaciated and barely recognizable.

Within his court Diocletian maintained a permanent body of legal advisers, men with significant influence on his re-ordering of juridical affairs.

On one occasion, Diocletian had to exhort a proconsul of Africa not to fear the consequences of treading on the toes of the local magnates of senatorial rank.

The fifth-century pagan Zosimus, by contrast, praised Diocletian for keeping troops on the borders, rather than keeping them in the cities, as Constantine was held to have done.

Diocletian therefore issued his Edict on Coinage, an act re-tariffing all debts so that the nummi, the most common coin in circulation, would be worth half as much.

In addition to his administrative and legal impact on history, the Emperor Diocletian is considered to be the founder of the city of Split in modern-day Croatia.

* Dioclesian, Henry Purcell's 1690 tragicomic semi-opera, loosely based on the life of the historical Diocletian

15 minute audio lecture on Diocletian.

The Principate ( 27 BC-284 AD ) period was succeeded by what is known as the Dominate ( 284 AD-527 AD ), during which Emperor Diocletian tried to put the Empire on a more formal footing.

A work on the martyrs of Palestine in the time of Diocletian was composed after 311 ; numerous fragments are scattered in legendaries which have yet to be collected.