The Syrian army accounted for three legions of the Roman army, defending the Parthian border. In the 1st century, it was the Syrian army that enabled Vespasian's coup. Syria was of crucial strategic importance during the crisis of the third century.
From the later 2nd century, the Roman senate included several notable Syrians, including Claudius Pompeianus and Avidius Cassius. In 193, the province was divided into Syria Coele. In the 3rd century, Syrians even reached for imperial power, with the Severan dynasty. From 260 to 273, Syria was part of the breakaway Palmyrene Empire.
Following the reforms of Diocletian, the two provinces became part of the Diocese of Oriens. Sometime between 330 and 350 (likely ca. 341), the province of Euphratensis was created out of the territory of Syria Coele along the western bank of the Euphrates and the former realm of Commagene, with Hierapolis as its capital. After ca. 415 Syria Coele was further subdivided into Syria I, with the capital remaining at Antioch, and Syria II or Salutaris, with capital at Apamea on the Orontes. In 528, Justinian I carved out the small coastal province Theodorias out of territory from both provinces.
The region remained one of the most important provinces of the Byzantine Empire. It was occupied by the Sassanids between 609 and 628, when recovered by the emperor Heraclius, but lost again to the advancing Muslims after the battle of Yarmouk and the fall of Antioch.
|Late Roman Provinces (4th–7th centuries)|
|Western Empire (395–476)|
Prefecture of Gaul
|Diocese of Gaul: Alpes Poeninae et Graiae • Belgica I • Belgica II • Germania I • Germania II • Lugdunensis I • Lugdunensis II • Lugdunensis III • Lugdunensis IV • Maxima Sequanorum|
Diocese of Vienne (later Septem Provinciae): Alpes Maritimae • Aquitanica I • Aquitanica II • Narbonensis I • Narbonensis II • Novempopulania • Viennensis
Diocese of Spain: Baetica • Baleares • Carthaginensis • Gallaecia • Lusitania • Mauretania Tingitana • Tarraconensis
Diocese of Britain: Britannia I • Britannia II • Flavia Caesariensis • Maxima Caesariensis • Valentia (369)
Prefecture of Italy
|Diocese of Suburbicarian Italy: Apulia et Calabria • Bruttia et Lucania • Campania • Corsica • Picenum Suburbicarium • Samnium • Sardinia • Sicilia • Tuscania et Umbria • Valeria|
Diocese of Annonarian Italy: Alpes Cottiae • Flaminia et Picenum Annonarium • Liguria et Aemilia • Raetia I • Raetia II • Venetia et Istria
Diocese of Africa†: Africa proconsularis (Zeugitana) | Byzacena • Mauretania Caesariensis • Mauretania Sitifensis • Numidia Cirtensis • Numidia Militiana • Tripolitania
Diocese of Pannonia (later of Illyricum): Dalmatia • Noricum mediterraneum • Noricum ripense • Pannonia I • Pannonia II • Savia • Valeria ripensis
|Eastern Empire (395–ca. 640)|
Prefecture of Illyricum
|Diocese of Dacia: Dacia Mediterranea • Dacia Ripensis • Dardania • Moesia I • Praevalitana|
Diocese of Macedonia: Achaea • Creta • Epirus nova| Epirus vetus | Macedonia I • Macedonia II Salutaris • Thessalia
Prefecture of the East
|Diocese of Thrace: Europa • Haemimontus • Moesia II§ • Rhodope • Scythia§ • Thracia|
Diocese of Asia*: Asia • Caria§ • Hellespontus • Insulae§ • Lycaonia (370) • Lycia • Lydia • Pamphylia • Pisidia • Phrygia Pacatiana • Phrygia Salutaria
Diocese of Pontus*: Armenia I* • Armenia II* • Armenia Maior* • Armenian Satrapies* • Armenia III (536) • Armenia IV (536) • Bithynia • Cappadocia I* • Cappadocia II* • Galatia I* • Galatia II Salutaris* • Helenopontus* • Honorias* • Paphlagonia* • Pontus Polemoniacus*
Diocese of the East: Arabia • Cilicia I • Cilicia II • Cyprus§ • Euphratensis • Isauria • Mesopotamia • Osroene • Palaestina I • Palaestina II • Palaestina III Salutaris • Phoenice • Phoenice Libanensis • Syria I • Syria II Salutaris • Theodorias (528)
Diocese of Egypt: Aegyptus I • Aegyptus II • Arcadia • Augustamnica I • Augustamnica II • Libya Superior • Libya Inferior • Thebais Superior • Thebais Inferior
|Other territories||Taurica • Lazica (532/562) • Spania (552)|
|Notes||Provincial administration reformed by Diocletian, ca. 293. Praetorian prefectures established after the death of Constantine I. Empire permanently partitioned after 395. Exarchates of Ravenna and Africa established after 584. After massive territorial loss due to the Muslim conquests, the remaining provinces were superseded by the theme system in ca. 640–660, although they survived under the latter until the early 9th century|
* affected (boundaries modified/abolished/renamed) by Justinian's administrative reorganization in 534–536
† re-established after reconquest by the Eastern Empire in 534, as the separate praetorian prefecture of Africa
§ joined together into the Quaestura exercitus in 536