| Praetorian prefecture of Illyricum Praefectura praetorio per Illyricum Ἐπαρχότης Ἰλλυρικοῦ | |
|---|---|
| Praet. prefecture of theEastern Roman Empire | |
| 347–630s | |
 The praetorian prefecture of Illyricum (375–379) | |
| Capital | Sirmium, laterThessalonica |
| Historical era | Late antiquity |
• Established | 347 |
• Loss of most of Illyricum toSlavic incursions | 630s |
| Political subdivisions | Diocese of Macedonia Diocese of Dacia Diocese of Pannonia(until 379) |
Thepraetorian prefecture of Illyricum (Latin:praefectura praetorio per Illyricum;Greek:ὑπαρχία τῶν πραιτωρίων τοῦ Ἰλλυρικοῦ, also termed theprefecture of Illyricum) was one of fourpraetorian prefectures into which theLate Roman Empire was divided.
The administrative center of the prefecture wasSirmium from 375 to 379, thenThessalonica.[1][2] The prefecture took its name from the olderprovince of Illyricum, which in turn was named after ancientIllyria. In its greatest expanse it encompassedPannonia,Noricum,Crete, and most of theBalkan peninsula except forThrace.[3]
Unlike the other three classical prefectures listed in theNotitia Dignitatum—Gaul, theItaly–Africa and theEast—the fourth-century history of Illyricum as a prefecture involved abolition, re-establishment, and repeated division.[4][5] Later writers created the impression that Constantine I established territorial prefectures early in the fourth century, but contemporary practice kept thepraetorian prefect as the emperor's chief of staff, and only by the mid-fourth century did the prefectures become enduring territorial units.[5]
Initially the territories later grouped as Illyricum belonged to thePrefecture of Italy, Illyricum and Africa. The Illyrian dioceses were set apart as a praetorian prefecture in their own right during the struggles among Constantine's sons after his death in 337.[6] The dioceses ofMacedonia,Dacia, andPannonia were probably first grouped together in 347 byConstans, when they were detached from the Italian prefecture. Some scholars prefer an earlier stage in 343, when Constans appointed a separate prefect for Italy, which implies a corresponding rebalancing in the Danubian and Balkan provinces.[5]
The prefecture existed until 361, whenJulian abolished it. It was revived underGratian between 375 and 379.[2] In 379 the Diocese of Pannonia, often calledIllyricum occidentale or Western Illyricum, was reassigned to the Italian sphere as theDiocese of Illyricum, while Macedonia and Dacia, the so-calledIllyricum orientale, were ruled directly byTheodosius I from Thessalonica for a short period.[7] During 384–395 the two eastern dioceses were once more attached to the Italian prefecture, except for 388–391, when they again formed a separate Illyrian prefecture.[6]
After Theodosius's death in 395 and the final division of the Empire, Illyricum assumed the permanent form shown in theNotitia, comprising the dioceses of Macedonia and Dacia, with Thessalonica as capital.[4] TheWestern Roman Empire continued to claim these dioceses, especially under the regency ofStilicho, until 437 when, as part of the dowry ofLicinia Eudoxia,Valentinian III recognized Eastern control over the prefecture.[3] Some scholars place the prefectural seat at Sirmium again between 437 and 441, although this relocation is debated because the northern Balkans were then destabilized by invasions.[1]Justinian I later elevatedJustiniana Prima, but proposals to shift the prefectural center there did not take effect.[2]
Following the Slavic incursions in the later sixth and seventh centuries, most of the Balkan hinterland slipped from imperial control. The government retained Thrace nearConstantinople,Thessalonica and its environs, and coastal Greece.[2][8] The pressures of theByzantine–Bulgarian Wars led to reorganization. By the early ninth centuryThessalonica formed a distinct theme under astrategos and the old prefectural framework had vanished from practical administration.[7]
