Praetorian prefecture of Illyricum

The praetorian prefecture of Illyricum (Latin: praefectura praetorio per Illyricum; Greek: ὑπαρχία τῶν πραιτωρίων τοῦ Ἰλλυρικοῦ, also termed the prefecture of Illyricum) was one of four praetorian prefectures into which the Late Roman Empire was divided. The administrative center of the prefecture was Sirmium from 375 to 379, then Thessalonica.

Source: Wikipedia — Praetorian prefecture of Illyricum (CC BY-SA 4.0)