In Latin, Gallia was also sometimes used as a general term for all Celtic peoples and their territories, such as all Brythons, including Germanic and Iberian provinces that also had a population with a Celtic culture. The plural, Galliarum in Latin, indicates that all of these are meant, not just Caesar's Gaul.
Viennensis was named after the city ofVienna, and almost entirely in present-day France, roughly south of the Loire. It was originally part of Caesar's newly conquered province of Transalpine Gaul, but a separate diocese from the start.
[[Praetorian prefecture of Italy|Praetorian prefecture of Italy and Africa (western)]]
Originally there was a single diocese of Italia, but it was eventually split into a northern section and a southern section. The division of Italy into regions had already been established by Aurelian.
Pannonia was one of the two dioceses in the eastern quarters of the Tetrarchy not belonging to the cultural Greek half of the empire ; It was transferred to the western empire when Theodosius I fixed the final split of the two empires in 395.
The Dacians had lived in the Transylvania area, annexed to the Empire by Trajan. However, during the invasions of the third century Dacia was largely abandoned. Some inhabitants evacuated from the abandoned province settled on the south side of the Danube. They renamed their new homeland Dacia to diminish the impact that abandoning the original Dacia had on the Empire's prestige. The diocese was transferred to the western empire in 384 by Theodosius I, probably in partial compensation to the empress Justina for his recognition of the usurpation of Magnus Maximus in Britannia, Gaul and Hispania.
The Diocese of Macedonia was transferred to the western empire in 384 by Theodosius I, probably in partial compensation to the empress Justina for his recognition of the usurpation of Magnus Maximus in Britannia, Gaul and Hispania.
As the rich home territory of the eastern emperor, the Oriens prefecture would persist as the core of the Byzantine Empire long after the fall of Rome. Its praetorian prefect would be the last to survive, but his office was transformed into an essentially internal minister.
Asia in Antiquity stood for Anatolia. This diocese centred on the earlier Roman province of Asia, and only covered the rich western part of the peninsula, mainly near the Aegean Sea.
Pontus is the Latinized form of Greek Pontos, the name of a Hellenistic kingdom, which in turn is derived from the Euxine Pontus, the Greco-Roman name of the Black Sea. It mainly contains parts of Asia minor near those coasts, but also includes the north of very variable border with Rome's enemy Parthia/Persia.
The Eastern diocese shares its geographic name with the prefecture, even after it lost its rich part, Egypt, becoming a separate diocese; but militarily crucial on the Persian border and unruly desert tribes. It comprised mainly the modern Arabic Mashriq except for the desert hinterland:
This diocese, comprising north eastern Africa—mainly Egypt, the rich granary and traditional personal domain of the emperors—was the only diocese that was not under a vicarius, but whose head retained the unique title of Praefectus Augustalis. It was created by a split of the diocese of Oriens. All but one, the civilian governors were of the modest rank of Praeses provinciae.
Aegyptus came to designate Lower Egypt around Alexandria. Originally it was named Aegyptus Iovia. Later it was divided into two provinces
Augustamnica was the remainder of Lower Egypt, together with the eastern part of the Nile delta – the only Egyptian province under a Corrector, a lower ranking governor. Originally it was named Aegyptus Herculia. Later it was divided in two provinces
Thebais was Upper Egypt. Nubia south of Philae had been abandoned to tribal people. Later it was divided into two provinces, Superior and Inferior.
Apart from modern Egypt, Aegyptus also comprised the former province of Cyrenaica, being the east of modern Libya. Cyrenaica was split into two provinces, each under a praeses:
