The Roman empire in the time of Hadrian (ruled 117-38 AD), showing, in western Asia, the imperial province of Syria (Syria/Lebanon). 4 legions deployed in 125
Syria was a Roman province, annexed in 64 BC by Pompey, as a consequence of his military presence after pursuing victory in the Third Mithridatic War. It remained under Roman, and subsequently Byzantine, rule for seven centuries, until 637 when it fell to the Islamic conquests.
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 and Syria Phoenice. 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.
In the 4th century, under Theodosius I, Syria Coele was further subdivided into Syria, Syria Salutaris, and Syria Euphratensis), while Syria Phoenice was divided into Phoenice and Phoenicia Libanesia.
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 replaced by the Theme system after ca. 660
* 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