Diocletion abandoned the title “Princeps” in favour of the title “Dominus”, which historically had been the title slaves gave to their master! All this without any written definition of a constitution. The image of the continuance of the Republic was projected by the concept that all the roles and powers and counterbalances were still in place but now invested in one person , the Emperor himself.
The change from Republic to Principate to Dominate was a gradual evolution but the changes were nevertheless real.
Thus the peripheral provinces such as Britain, and there were now four separate provinces in Britain alone, did not responded to the Senate in Rome, but only to the Emperor directly. This caused no concern as the machinations of Rome and its Senate had always seemed like the activities of a foreign state of no concern to the British, or the citizens of Gaul, Hispania or Mauretania. Now it was only a question of choosing the high king as emperor.
Diocletian’s went still further, he accepted the inevitable he learned from instability and from the successful experiment under the reign of Marcus Aurelius. He created the concept of two parallel empires, jointly owned by two Augusti. It was envisaged that the Augusti would consult each other on all important issues but only in the vaguest terms. No attempt was made to define what an important issue might be. Diocletion also learned from the Albinus Experiment which had come close to success. He created the post of “Caesar’, one for each half of the empire.
He could have achieved control in an entirely different way. his decision was based on a recognition that there really were two different empires, east and west.
The Celts had made their point and now it seemed they had got what they wanted.
Diocletion set up the original template for his reform. He made himself Eastern Augustus and appointed his long term associate Maximian as Caesar for the west.
Maximian was however from Sirmium, a roman town in pannonia . He was an eastern Celt. He had no feeling for western celtic sensibilities and made no attempt to establish his credentials as “high king”
Maximian appointed Mausaeus Carausius to control the activivities of the Frankish and Saxon pirates in the English channel. Carausius succeed brilliantly and strenghened coastal defences both in Britain and Gaul. his success attracted celtic support and soon he felt able to declare himself western Augustus, superior to Maximian. He then styled himself as Emperor of “Imperium Britanniarum” and issued coins as such. His success continued and he extended his empire to include north-west gaul. The gallic empire was reborn.
Maximian promoted himself to be Augustus of the west but made no effective moves against Carausius preffering to attack Burgundians, Allemanni, Heruli and Chaibones along the Rhine frontier.
In 288 Diocletian appointed Constantius Chlorus as a legate (possibly a comes) to attack the Franks in the Rhine delta who had made themselves allies of Causaurius. The declared purpose was so that a seaborne attack on Britain could be mounted from bases on the Rhine. Constantius defeated the Franks and siezed their territory but the attack on Britain did not take place.
As a result of his success Constantius Chlorus was appointed Caesar of the west and at the same time a military contemporary Galerius was appointed Caesar of the east. Constantius divorced Helen and married Maximian’s step daughter Theodora.
Diocletians planned reorganisation was now complete. The sons of Constantius and Maximian took up residence with Diocletian in Nicomedia (Asia Minor). They were obviously intended to be the eventual successors to their fathers territories.
Constantius Chlrorus invaded and defeated the ‘Imperium Brittanicum’
In 305 Diocletian retired, the only Emperor ever to do so. He died in 311, living long enought to see the objectives of his reforms come to nothing.
He forced Maximian to retire with him probably to test out his succession planning.
This attempt to improve succession planning envisaged the Caesar in each half of the Empire would work as an assistant to the Augustus and thus be a ready trained replacement. Subsequent events make it clear that it was intended that the agreement of both Augustii was needed to appoint a new Caesar but not even this was documented.
In practice this reform creating not two but four parallel empires. Again it was not formally documented and there was disputation about the boundaries. It was a recipe for conflict. The subdivision itself had built in inequities.
A flawed concept
The objectives of Diocletian’s reforms are clear. He recognised the requirement for a different style of leadership in both halves of the empire and to provide a structured succession to avoid internal conflict.
It took over a hundred years for the subdivision to become a reality and in the meantime the Augusti and the Caesars yet more civil wars to seek a greater share of resources or obtain total control.
The problems started immediately Constantius became Augustus of the West and Galerius Augustus in the East. The East included Italia, leaving the Gallic empire as a totally seperate entity. It had been supposed but not formally agreed that Constantius’ son Constantine and Maximian’s son Maxentius would be nominated as Caesars.
Galerius protested that they were both “of the west” and nominated his own nephew Maximin Daia as Caesar of the east. This left only one position for either Constantine or Maxentius an almost impossible decision. Instead of either of them a default candidate Severus was selected, yet another of the military group which had served Diocletian. Galerius moved immediatly to Nicomedia where he hoped he would have control of both Constantine and Maxentius. He may have intended to dispose of them, but if so he acted too slowly they both fled. Maxentius to Rome and Constantine to Britain.
Legend has it that in his flight to Britain Constantine used post horses and at each post stop he ham-strung all other horses to prevent pursuit.
In Britain he joined his father and joined him in a campaign to drive the Picts back beyond Hadrian’s wall.
Contantius was taken ill and died at York less than a year later. Galerius declared Severus the Augustus of the west , an appointment which was immediately rejected by both the British and the legions in Britain.
Constantine sent to Galerius, a picture of himself wearing the purple and the imperial wreath. Galerius refused to confirm Constantine as Augustus but instead offered him the role of Caesar with control of Britain, Gaul and Hispania Serverus was left as the senior emperor but controlling only the italian peninsula and africa.
Once again the Gallic empire was reborn.
Meanwhile in 306 Maximian emerged from retirement declared himself Augustus and his disenfrachised son Maxentius, Caesar and “Prince of the Romans”. Severus invaded Italy but was defeated and ultimately executed. Incredibly father and son then fell out and Maximian fled to Consantine’s capital at Trier( more echo’s of the gallic empire). Constantine was already Maximian’s step grandson and as a result of this visit agreed to marry Maximian’s daughter Fausta, thus also becoming his son in law.
Diocletion intervened from retirement in an attempt to salvage the wreckage of his succession reforms . Maximian was again persuaded to retire but an associate of Gallerius, Licinius was appointed as Augustus for the West. Both Constantine and Maxentius refused to accept the appointment and Maximin Dia declared himselt Augustus for the orient so for a short period there were Five Augusti.