It was originally part of Caesar's newly conquered province of Transalpine Gaul,[citation needed] but a separate diocese from the start.
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 ("East") prefecture would persist as the core of the Byzantine Empire long after the fall of Rome.
This diocese (the name means 'the Asian ones') centred on the earlier Roman province of Asia, and only covered the rich western part of the peninsula, mainly near the Aegean Sea.
It mainly contains parts of Asia minor near those coasts (as well as the mountainous centre), but also includes the north of very variable border with Rome's enemy Parthia/Persia.
It comprised mainly the modern Arabic Mashriq (Syria, Lebanon, Iraq, Israel, the Palestinian Territories and Jordan) except for the desert hinterland: Further it contained the southeastern coast of Asia Minor and the close island of Cyprus This diocese, comprising northeastern 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.