A further massive transfer of Bastarnae was carried out by emperor Diocletian ( ruled 284-305 ) after he and his colleague Galerius defeated a coalition of Bastarnae and Carpi in 299.

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

Galerius, meanwhile, was engaged during 291 – 293 in disputes in Upper Egypt, where he suppressed a regional uprising.

In a public ceremony at Antioch, the official version of events was clear: Galerius was responsible for the defeat ; Diocletian was not.

Galerius was reinforced, probably in the spring of 298, by a new contingent collected from the Empire's Danubian holdings.

Narseh retreated to Armenia to fight Galerius ' force, to Narseh's disadvantage ; the rugged Armenian terrain was favorable to Roman infantry, but unfavorable to Sassanid cavalry.

Diocletian was conservative in matters of religion, a man faithful to the traditional Roman pantheon and understanding of demands for religious purification, but Eusebius, Lactantius and Constantine state that it was Galerius, not Diocletian, who was the prime supporter of the purge, and its greatest beneficiary.

Antioch was Diocletian's primary residence from 299 to 302, while Galerius swapped places with his Augustus on the Middle and Lower Danube.

Diocletian believed that Romanus of Caesarea was arrogant, and he left the city for Nicomedia in the winter, accompanied by Galerius.

Rumors alleging that Diocletian's death was merely being kept secret until Galerius could come to assume power spread through the city.

Afterward, the persecutions under Diocletian and Galerius directed his attention to the martyrs of his own time and the past, and this led him to the history of the whole Church and finally to the history of the world, which, to him, was only a preparation for ecclesiastical history.

In 293, feeling more focus was needed on both civic and military problems, Diocletian, with Maximian's consent, expanded the imperial college by appointing two Caesars ( one responsible to each Augustus ) — Galerius and Constantius Chlorus.

* Sirmium ( modern Sremska Mitrovica ) in the Vojvodina region of modern Serbia, and near Belgrade, on the Danube border ) was the capital of Galerius, the eastern Caesar ; this was to become the Balkans-Danube prefecture Illyricum.

When Constantius died in 306, Galerius promoted Severus to Augustus while Constantine the Great was proclaimed Augustus to succeed his father Constantius, by his father's troops.

The first book sketches briefly the history of the early Roman emperors from Augustus to Diocletian ( 305 ); the second, third and fourth deal more fully with the period from the accession of Constantius Chlorus and Galerius to the death of Theodosius I ; the fifth and sixth, the most useful for historians, cover the period between 395 and 410, when Priscus Attalus was deposed ; for this period, he is the most important surviving non-ecclesiastical source.

On September 13, 258, he was imprisoned at the behest of the new proconsul, Galerius Maximus.

When the Roman Empire was divided into the tetrarchy, Thessaloniki became the administrative capital of one of the four portions of the Empire under Galerius Maximianus Caesar, where Galerius commissioned an imperial palace, a new hippodrome, a triumphal arch and a mausoleum among others.

Narseh moved south into Roman Mesopotamia in 297, where he inflicted a severe defeat on Galerius in the region between Carrhae ( Harran, Turkey ) and Callinicum ( Ar-Raqqah, Syria ) ( and thus, the historian Fergus Millar notes, probably somewhere on the Balikh River ).

* Galerius makes preparations in Syria for a campaign against the Persian king Narseh.

Galerius crosses the Euphrates into Syria to join Diocletian at Antioch.

Narseh then moved south into Roman Mesopotamia, where he inflicted a severe defeat on Galerius, then commander of the Eastern forces, in the region between Carrhae ( Harran, Turkey ) and Callinicum ( Ar-Raqqah, Syria ).

In 305, his maternal uncle Galerius became the eastern Augustus and adopted Maximinus, raising him to the rank of caesar ( in effect, the junior eastern Emperor ), with the government of Syria and Egypt.

Galerius crossed the Euphrates into Syria to join his father-in-law Diocletian at Antioch.

Galerius ended the persecution in the East in 311, but it was resumed in Egypt, Palestine, and Asia Minor by his successor, Maximinus.

* Galerius, Roman Caesar in the Balkan, is dispatched to Egypt to fight against the rebellious cities Busiris and Coptos.

Soon after his appointment, Galerius would be dispatched to Egypt to fight the rebellious cities Busiris and Coptos.

Since it was Galerius's army that would have been purged — Diocletian had left his in Egypt to quell continuing unrest — Antiochenes would understandably have believed Galerius to be its instigator.

In the spring of 293, in either Philippopolis ( Plovdiv, Bulgaria ) or Sirmium, Diocletian would do the same for Galerius, husband to Diocletian's daughter Valeria, and perhaps Diocletian's praetorian prefect.

Diocletian publicly humiliated Galerius, forcing him to walk for a mile at the head of the Imperial caravan, still clad in the purple robes of the Emperor.

Narseh sent an ambassador to Galerius to plead for the return of his wives and children in the course of the war, but Galerius had dismissed him.

Diocletian argued that forbidding Christians from the bureaucracy and military would be sufficient to appease the gods, but Galerius pushed for extermination.

Galerius left the city for Rome, declaring Nicomedia unsafe.

After suffering a defeat by the Persians in 296, Galerius crushed Narseh in 298 — reversing a series of Roman defeats throughout the century — capturing members of the imperial household and a substantial amount of booty and gaining a highly favourable peace treaty, which secured peace between the two powers for a generation.

* Peace of Nisibis: Galerius signs a treaty with the Persian king Narseh that will last for 40 years.

The city subsequently expanded for a century and a half, it became a significant political and economical centre, moreso — it became one of the first Roman cities where Christianity was recognized as an official religion ( Еmperor Galerius ).

Diocletian may or may not have been present at the battle, but would present himself soon afterwards at Antioch, where the official version of events was made clear: Galerius was to take all the blame for the affair.

Their marriage was the occasion for the jointly-issued " Edict of Milan " that reissued Galerius ' previous edict allowing Christianity to be professed in the Empire, with additional dispositions that restored confiscated properties to Christian congregations and exempted Christian clergy from municipal civic duties. The redaction of the edict as reproduced by Lactantius-who follows the text affixed by Licinius in Nicomedia on June 14 313, after Maximinus ' defeat-uses a neutral language, expressing a will to propitiate " any Divinity whatsoever in the seat of the heavens ".

Maximinus has a bad name in Christian annals, as having renewed persecution after the publication of the toleration edict of Galerius ( see Edict of Toleration by Galerius ), acting outwardly as responding to the demands of various urban authorities asking for the expelling of Christians.

Some sources ( Lactantius, Epitome ) state that Galerius hated Maxentius and used his influence on Diocletian that Maxentius be ignored in the succession ; maybe Diocletianus also thought that he was not qualified for the military duties of the imperial office.

On his arrival at Antioch, Galerius was rebuked by Diocletian who disgraced him for his shameful defeat at the hands of Narses.

Artistic license was taken in the representations, for instance, the Caesar Galerius is shown in personal combat with the Sassanid Shah Narses in one of the panels ; although they never met in battle.

Porphyry is also known as an opponent of Christianity and defender of Paganism ; his defense of traditional religion, Philosophy from Oracles, written before the persecutions of Christians under Diocletian and Galerius, set out the basis for them: