[1][2][3] The classical administrative model, as exemplified by the Notitia Dignitatum, divided the late Roman Empire into provinces, which in turn were grouped into dioceses and then into praetorian prefectures.
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.
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.
Gradually however, the themes superseded the provinces, the last vestiges of which were abolished in the early 9th century inspired in part by the Hellenistic pagarchies and nomarchies of late Roman Egypt.
Peripheral territories, often with a strong maritime character like Crete, Crimea or Cephallenia were run by archons as in classical Greek times and are hence known as archontates (archontiai, sing.
With the great military expansion of the 10th and early 11th centuries, new themes were established as land was recovered from the Arabs in the East and after the conquest of Bulgaria.
In the Empire of Trebizond, the old banda of the theme of Chaldia remained extant, and formed the country's sole administrative subdivision.