Subdivisions of the Byzantine Empire

The East Roman or Byzantine Empire (330–1453) had a developed administrative system, which can be divided into three major periods: the late Roman/early Byzantine, which was a continuation and evolution of the system begun by the emperors Diocletian and Constantine the Great, which gradually evolved into the middle Byzantine, where the theme system predominated alongside a restructured central bureaucracy, and the late Byzantine, where the structure was more varied and decentralized and where feudal elements appeared.

The classic Diocletianian/Constantinian model, as exemplified by the Notitia Dignitatum, divided the Roman Empire into provinces (in Greek επαρχία, eparchy), which in turn were grouped into dioceses and then into praetorian prefectures.

The system remained intact until the 530s, when Justinian I (r. 527–565) undertook his administrative reforms. He effectively abolished the dioceses, merged smaller provinces and created new types of jurisdictions like the quaestura exercitus, which combined civil with military authority, thus overturning the main principle of the Diocletianic system.

Under Maurice (r. 582–602), this was carried a step further with the exarchates of Italy and Africa, which became effectively semi-autonomous territories.

The traditional administrative system faced a severe challenge in the first half of the 7th century, when the Muslim conquests and the invasion of the Balkans by the Slavs led to extensive territorial loss. The only major contiguous territory remaining to the Empire was Asia Minor, and there in the period 640–660 the first themes (themata, sing. thema) were established. Initially these were simply military jurisdictions, reflecting the area that each of the Byzantine army's field armies occupied; underneath the themes and their strategoi, the old provinces continued to serve as the main administrative and fiscal units. Gradually however, the themes superseded the provinces, the last vestiges of which were abolished in the early 9th century. Each theme had a regular structure, being divided along military lines into tourmai, droungoi and banda. The droungos however was only a military, not an administrative division.

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