Successive administrative reforms in Late Antiquity led to the creation of a system of themes, which first appeared in Asia Minor in the 7th century and had extended to the remaining provinces of the Byzantine Empire by the beginning of the 9th.
At the end of the 7th century, the theme of Hellas was created within the prefecture of Illyricum. It embraced western and central Macedonia, while eastern Macedonia (part of the prefecture of the East) was included in the theme of Thrace. Early in the 9th century, the theme of Hellas was divided into smaller themes, among which was the theme of Thessalonike, with Thessalonike city as its capital; it comprised western and central Macedonia and a part of Thessaly.
In the same period the western part of the theme of Thrace (the area lying between the Strymon and Evros rivers) formed the theme of Macedonia, from which the theme of Strymon (the area between the Strymon and Nestos rivers) was detached in the late 9th century.