Lucius Verus's campaign Northern Mesopotamia, including
Osroene, came again under Roman control in the
expedition of
Lucius Verus in 161–166, but were not formally organized into provinces; instead, they were left under local vassal rulers, although Roman garrisons were maintained, notably at
Nisibis.
Year of the Five Emperors This control was threatened in 195, during the civil war between
Septimius Severus (r. 193–211) and the usurper
Pescennius Niger, when rebellions broke out in the area, and Nisibis was besieged. Severus quickly restored order and organized Osroene as a full province.
Reconquest by Severus Next, Severus embarked on a war against Parthia, which he concluded successfully with the
sack of the Parthian capital
Ctesiphon. In emulation of Trajan, he re-established a province of Mesopotamia in 198, with Nisibis, elevated to the status of a full
colonia, as its capital. Unlike Trajan's province, which encompassed the whole of Roman-occupied Mesopotamia between the Euphrates and Tigris rivers, the new province was limited between the province of
Osroene to the south, the Euphrates and Tigris to the north, and the river Chaboras (modern
Khabur) to the east.
Border conflict For the remainder of its existence, the province would remain a bone of contention between the Romans and their eastern neighbors, suffering heavily in the recurrent
Roman–Persian Wars. In the turmoil that followed the
Year of the Six Emperors, in 239–243,
Ardashir I (r. 224–241), the founder of the new
Sassanid Empire which replaced the moribund Parthians, attacked and overran the area, but it was
recovered by
Timesitheus before his death in 243. In the 250s, the Persian shah
Shapur I (r. ca. 240–270) attacked Mesopotamia, and fought with the Roman emperor
Valerian (r. 253–260), whom he
captured at
Edessa in 260. In the next year, however,
Odaenathus of
Palmyra took a stand against Shapur, who eventually retreated. == Diocletianic-Constantinian reorganization ==