Emperor Aurelian (270-275), confronted with the secession of Gallia and Hispania from the empire since 260, with the advance of the Sassanids in Asia, and the devastations that the Carpians and the Goths had created in Moesia and Illyria, abandoned the province of Dacia created by Trajan and withdrew his troops altogether, fixing the Roman frontier at the Danube. A new Dacia Aureliana was organised south of the Danube out of central Moesia, with its capital at Serdica.
The abandonment of Dacia Traiana by the Romans is mentioned by Eutropius in his Breviarium historiae Romanae, book IX :
The province of Dacia, which Trajan had formed beyond the Danube, he gave up, despairing, after all Illyricum and Moesia had been depopulated, of being able to retain it. The Roman citizens, removed from the town and lands of Dacia, he settled in the interior of Moesia, calling that Dacia which now divides the two Moesiae, and which is on the right hand of the Danube as it runs to the sea, whereas Dacia was previously on the left.
Creation
Dioceses of Dacia and Pannonia in 400 ADMap of the northern Balkans in the 6th century, including the Diocese of Dacia and its provinces.
During the administrative reforms of Diocletian (284-305), the Diocese of Moesia was created, encompassing most of the central Balkans and the Greek peninsula. Later, however, probably in the time of Constantine the Great (306-337) the diocese was split in two, forming the Diocese of Macedonia in the south and the Diocese of Dacia, in the north.
The Diocese of Dacia was composed of five provinces: Dacia Mediterranea (the southern, interior portion of Dacia Aureliana), Dacia Ripensis (the northern, Danubian portion of Dacia Aureliana), Moesia Prima (the northern portion of Moesia Superior), Dardania (the southern portion of Moesia Superior) and Praevalitana (the eastern portion of Dalmatia).
In 535, under emperor Justinian I (527-565), ecclesiastical order on the territory of the diocese was reshaped, and new Archbishopric of Justiniana Prima was created, centered in emperor's birth city of Justiniana Prima. Newly appointed archbishop was given metropolitan jurisdiction over all provinces of the Diocese of Dacia.[1]
Destruction
The territory of diocese was devastated by the Huns in the middle of 5th century and finally overrun by the Avars and Slavs in late 6th and early 7th century.[2]
Procopius. Edited by H. B. Dewing. 7 vols. Loeb Classical Library. Cambridge, Massachusetts: Harvard University Press and London, Hutchinson, 1914–40. Greek text and English translation.
Maurice's Strategikon: Handbook of Byzantine Military Strategy. translated by George T. Dennis. Philadelphia 1984, Reprint 2001.
As found in the Notitia Dignitatum. Provincial administration reformed and dioceses established by Diocletian, c. 293. Permanent praetorian prefectures established after the death of Constantine I. Empire permanently partitioned after 395. Exarchates of Ravenna and Africa established after 584. After massive territorial losses in the 7th century, the remaining provinces were superseded by the theme system in c. 640–660, although in Asia Minor and parts of Greece they survived under the themes until the early 9th century.
