The potential for spltting the empire between western (Roman/Celtic) and eastern (Greek) halves had been clear since the time of Octavian and Antony. One last attempt to hold it all together was made by Diocletian - and his "tetrarch" system - an Augustus (senior) and a Caesar (apprentice) for east and west. Despite some chaos after Diocletian retired, power eventually passed again to one man - Constantine the Great. But by moving the centre of power to Constantinople, he ultimately made the final split more likely.

Inspired by a vision ("in hoc signo vinces" - with this device you will conquer) Constantine had his men paint the sign of the cross on their shields. They went on to win a decisive vicory over the rival emperor Maxentius at the Milvian Bridge.



Diocletian. (Ny Carlsberg Glyptotek: René Seindal)

One aspect of the problem was that the empire had always consisted of two parts. Much of the region comprising Macedonia and Cyrenaica and the lands to east was Greek, or had been Hellenized before being occupied by Rome. The western part of the empire had received from Rome its first taste of a common culture and language overlaid on a society which was largely Celtic in origin.

In AD 286 Diocletian split the empire into east and west, and appointed a Dalmatian colleague, Maximian (d. AD 310), to rule the west and Africa. A further division of responsibilities followed in AD 292. Diocletian and Maximian remained senior emperors, with the title of Augustus, while Galerius, Diocletian’s son-in-law, and Constantius (surnamed Chlorus, “the Pale”) were made deputy emperors with the title of Caesar. Galerius was given authority over the Danube provinces and Dalmatia, while Constantius took Britain, Gaul and Spain. Diocletian retained all his eastern provinces and set up his regional headquarters at Nicomedia in Bithynia, where he held court like an eastern potentate.

The tetrarchs

The tetrarchs, (left) Diocletian and Maximian, (behind) Constantius and Galerius. Porphyry sculpture of AD 305, Piazza san Marco, Venice. (VRoma: AICT)

The establishment of an imperial executive team had less to do with delegation than with the need to exercise closer supervision over all parts of the empire, and thus to lessen the chances of rebellion. There had already been trouble in the north-west, where in AD 286 the commander of the naval forces at Boulogne, Aurelius Carausius [see note in column on right], to avoid execution for embezzling stolen property, proclaimed himself an emperor, set himself up as ruler of Britain, and even issued his own coins. This outbreak of lèse-majesté was not finally obliterated until AD 296.


Caracalla had introduced the antoninianus, a silver coin worth two denarii, which gradually became debased. By c. AD 293 - 6, the date of this particular coin, the metal was simply an alloy. It was minted in Britain by Allectus, who murdered Carausius in AD 293 and usurped his unconstitutional role. The figure, and the letters round the rim, stand for peace. The ten-year rebellion was put down by Constantius in AD 296. The letters ML stand for Moneta Londiniensis (Mint of London); established by Carausius, it was retained as an official source of issue until about AD 326. ( © Hunterian Museum and Art Gallery, University of Glasgow)

On 1 May AD 305 Diocletian took the unprecedented step of announcing from Nicomedia that he had abdicated; Maximian had no choice but to do the same. While Diocletian’s reign had been outwardly peaceful, the years of turmoil had left their mark on the administration of the empire and on its financial situation. He reorganized the provinces and Italy into 116 divisions, each governed by a rector or praeses, which were then grouped into twelve dioceses under a vicarius responsible to the appropriate emperor. He strengthened the army (at the same time purging it of Christians), and introduced new policies for the supply of arms and provisions. Diocletian’s monetary reforms were equally wide ranging, but though the new tax system he introduced was workable, if not always equitable, his bill in AD 301 to curb inflation by establishing maximum prices, wages, and freight charges fell into disuse, its effect having been that goods simply disappeared from the market.

Diocletians palace at Split

Reconstruction of Diocletian’s palace, Split, Croatia. (From Helen and Richard Leacroft, The Buildings of Byzantium, Brockhampton Press 1977)

Confident of his own safety, Diocletian had built for his retirement a palace near Salona in his native Dalmatia. Here he lived until his death in AD 313, gardening and studying philosophy, while refusing to take sides when the system of government he had devised almost immediately foundered.


Helena, a former barmaid, wife of Constantius Chlorus and mother of Constantine the Great. Constantius was subsequently forced to divorce her and marry Maximian’s daughter. (Capitoline Museums, Rome: René Seindal)

When he retired, Diocletian had promoted Galerius and Constantius to the posts of Augustus, and appointed two new Caesars. The troubles broke out when Constantius died at York in AD 306, and his troops proclaimed his son Constantine as their leader. Encouraged by this development, Maxentius, son of Maximian, had himself set up as emperor and took control of Italy and Africa, whereupon his father came out of his involuntary retirement and insisted on having back his former imperial command. At one point in AD 308 there seem to have been six men styling themselves Augustus, whereas Diocletian’s system allowed for only two. Galerius died in AD 311, having on his deathbed revoked Diocletian’s anti-Christian edicts. Matters were not fully resolved until AD 324, when Constantine defeated and executed his last surviving rival. The empire once again had a single ruler.

Constantine the Great

Bronze statue of Constantine, who was born in Naissus in Upper Moesia in about AD 272. (Capitoline Museums, Rome: René Seindal)

Constantine’s appellation “the Great” is justified on two counts. In AD 313, he initiated the Edict of Milan, which was now the administrative centre of Italy, giving Christians (and others) freedom of worship and exemption from any religious ceremonial. In AD 325 he assembled at Nicaea in Bithynia 318 bishops, each elected by his community, to debate and affirm some principles of their faith, resulting in the Nicene Creed. Though he was not baptized until just before his death in AD 337, he regarded himself as a man of the god of the Christians, and was thus the first Christian ruler. He also, in AD 330, established the seat of government of the Roman empire at Byzantium (which he renamed Constantinople, “City of Constantine”), thus ensuring that a Roman (but Hellenized and predominantly Christian) empire would survive the inevitable loss of its western part.

Sacrificial implements on a coin of Alexander Severus

Coin of Severus Alexander, depicting implements used in sacrifice. (© Hunterian Museum and Art Gallery, University of Glasgow)

To the Jews Constantine was ambivalent: while the Edict of Milan is known also as the Edict of Toleration, Judaism was seen as a rival to Christianity, and among other measures he forbade the conversion of pagans to its practices. In time he became even more uncompromising towards the pagans themselves, enacting a law against divination and finally banning sacrifices. He also destroyed temples and confiscated temple lands and treasures, which gave him much-needed funds to fuel his personal extravagances.

Procession through the arch of Constantine

Triumphal procession going through the Arch of Constantine in Rome, built in AD 315. Behind the arch is part of the Colosseum. (From Helen and Richard Leacroft, The Buildings of Ancient Rome, 1969)

Arch of Constantine

The Arch of Constantine today, with the Colosseum behind it. A photograph taken from much the same viewpoint as the drawing above. (VRoma: Paula Chabot)

A military commander of considerable dynamism, Constantine developed Diocletian’s reforms, and completed the division of the military into two arms: frontier forces, and permanent reserves, who could be sent anywhere at short notice. He disbanded the imperial guard, and established a chief of staff to assume control of all military operations and army discipline; the praetorian prefects, who had held military ranks while also being involved in civil affairs, under him became supreme appeal judges and chief ministers of finance.

Gold bar

Late fourth-century AD gold bar stamped four times with the name of the imperial accountant and also with that of the imperial assayer. Gold coins collected for taxes were immediately melted down, made into bars, and sent to the emperor’s residence to prevent pilfering by officials. (VRoma: British Museum: Barbara McManus)



Carausius was an army man who in his youth had piloted river boats along his native Belgian coast. In AD 285 or 286 he was put in charge of forcing out of business the Frankish and Saxon pirates who were ravaging coastal regions on both sides of the Channel. He concentrated his fleet at his headquarters at Boulogne, where it is suggested he used a novel form of combating the pirates. Through his intelligence network he obtained prior knowledge of where the next attack would be, and allowed it to take place. He would then ambush the pirates on their way home, and confiscate their booty, which he diverted to his personal treasury. It is said that when Maximian learned what was going on, he ordered the execution of Carausius.


Diocletian’s price and wage tariff

The comparisons between commodities are much as one might expect. Ordinary wine was twice the price of beer, and named vintages almost four times as much as vin ordinaire. Pork mince cost half as much again as beef mince, and about the same as prime sea fish. River fish were cheaper. A pint of fresh olive oil was more expensive than the same amount of vintage wine; there was a cheaper oil as well. Fattened goose was prohibitive; ten dormice cost about as much as one chicken. A carpenter could expect twice the wages of a farm labourer or a sewer cleaner. A teacher of shorthand or arithmetic could earn half as much again per pupil as an elementary-school teacher, who needed 30 students to earn as much as a carpenter; grammar-school teachers earned four times as much as an elementary teacher, and teachers of rhetoric five times as much. Baths’ attendants, those who guarded the clothes of bathers, and barbers were paid the same rate per customer. The carpenter needed to work for two days to earn enough to buy one peck of salt. A pair of women’s boots cost the same as a peck of peas.

Believe it or not:

As self-styled ruler of Britain, Carausius had the cheek to call himself Marcus Aurelius, and to issue a series of coins whose inscriptions referred to Diocletian, Maximian, and himself as the “three Augustuses”.

A fortuitous fog contributed to the final collapse of the rebel regime in Britain in AD 296. Allectus was killed in a battle against Constantius’s imperial guard, under its commander Julius Asclepiodotus, while Constantius was still on his way over. The fog caused part of Constantius’s division to divert to the port of London, which was on the point of being sacked by Frankish mercenaries from Allectus’s army, bent on retrieving some reward for their services before embarking for home. The citizens of London were treated to a gladiatorial show as the Franks were slaughtered. Constantius arrived too late to take part in the show, but not too late to take the credit for it.

Diocletian only visited Rome once, in AD 303, to celebrate his twentieth year in office.

Constantine introduced into Constantinople the kind of buildings to which he was accustomed. Circular buildings were discovered to be ideal for pilgrims, who could stand in circles around a central feature, such as a tomb. While the basilica, the covered hall, became in the hands of Constantine’s architects a dramatic ecclesiastical edifice.