At the end of the 3rd century AD, the Roman emperor
Diocletian divided the great Roman province of
Africa Proconsularis into three smaller provinces: Zeugitana in the north, still governed by a proconsul and referred to as Proconsularis; Byzacena to its adjacent south, and
Tripolitania to its adjacent south, roughly corresponding to southeast
Tunisia and northwest
Libya. Byzacena corresponded roughly to eastern Tunisia or the modern Tunisian region of
Sahel.
Hadrumetum (modern
Sousse) became the capital of the newly made province, whose governor had the rank of consularis. At this period the Metropolitan Archbishopric of Byzacena was, after the great metropolis
Carthage, the most important city in Roman (North) Africa west of
Egypt and its
Patriarch of Alexandria.
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 After massive territorial losses in the 7th century, the remaining provinces were superseded by the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.