Today marks the anniversary of an important transition in the history of the Roman Empire, one that would lead up to the legalization of Christianity within it. On this day in the year 293, the general Constantius Chlorus, the father of Constantine, was made the junior emperor of the West, as part of the system which historians now call the tetrarchy, the “rule of four.”

The half-century span from 235 AD, the year in which Emperor Alexander Severus was assassinated by his own troops, to 284, was an era of prolonged crisis for the Roman Empire. It is often described as a “military anarchy”, with one general after another contending for the imperial throne, and most emperors meeting a violent death at the hands of their successor after only a few years. The Empire also saw various barbarian invasions, severe economic instability, and a significant plague that lasted for 13 years. By the end of the 260s, it had broken into three separate states; these were reunited by the brief but highly effective reign of Emperor Aurelian (270-5), who was murdered after five years and several astonishingly successful military campaigns.

The man who finally began to restore some long-term stability was Diocletian, who became emperor in 284 and is now infamous as the last major persecutor of the Christians. Less than a year into his reign, he appointed a general named Maximian as his co-emperor, with the title of “Caesar”, while he himself as senior emperor was titled “Augustus.” Ten months later, Maximian’s title was changed to “Augustus”, making him de facto co-emperor. Whatever else his faults, Diocletian had the genius to recognize that the empire was too large for a single man to rule, and could better be governed by dividing power between an emperor and a vice-emperor.

This, however, did not resolve the problem of an eventual succession, which must have weighed heavily on his mind, given how many emperors had died violently in the decades before his accession. He therefore also instituted an orderly succession, by which each Augustus was given a junior co-emperor with the title “Caesar”. After twenty years, each Augustus would resign and be succeeded by his Caesar. If he died first, Caesar would finish Augustus’ term and appoint a successor. Diocletian’s plan was first put into action with the appointment of Constantius Chlorus as Maximian’s Caesar on March 1st, 293, the two of them ruling the western half of the Empire. A general named Galerius became Diocletian’s Caesar and co-ruler of the East twenty days later.

No one will be surprised to read that this system did not last long beyond the first peaceful transition. Diocletian and Maximian both resigned in 305; Chlorus became Augustus of the West, with a Caesar named Valerius Severus, and Galerius of the East, with his Caesar Maximin Daia. Chlorus’ troops, however, refused to recognize anyone other than Constantius’ son Constantine as emperor, leading to another round of civil war, which is a tale for another time. Suffice it to say for now that Constantine would eventually become sole emperor first of the West, then of the whole Empire, and in 313, legalize the Christian religion which had been so recently and so fiercely persecuted.

When Constantine founded his new capital on the site of the ancient Greek port of Byzantium, he decorated its public buildings and spaces with works of art brought from all over the empire. Among these was an image of the four tetrarchs made of Egyptian porphyry, a stone that was highly prized both because of its color, which symbolized royalty to the Romans, and its extreme durability. The place from which it was brought is unknown, but Constantine had it set up in a public square called the “Philadelpheion – the place of brotherly love.” It remained there for almost 800 years, until the city was sacked by the Venetians in 1204, and many of its treasures, including this statue group, were brought back to Venice. It was installed in a corner of the façade of St Mark’s Basilica; a Venetian legend claims that there were four thieves who attempted to steal some of the basilica’s treasures and were petrified by St Mark as a warning to other miscreants. The piece missing at the lower right was found near the site of the Philadelpheion in 1965 and is now in the Istanbul Archeological Museum.

(Photo from Wikimedia Commons by Rino PorrovecchioCC BY-SA 2.0