In 165, Roman forces, perhaps led by Martius Verus and the V Macedonica, moved on Mesopotamia.
Edessa was re-occupied, Mannus re-installed.
His coinage resumed, too: 'Ma'nu the king' (Syriac: M'NW MLK') or Antonine dynasts on the obverse, and 'King Mannos, friend of Romans' (Greek: Basileus Mannos Philorōmaios) on the reverse.
The Parthians retreated to Nisibis, but this too was besieged and captured.
The Parthian army dispersed in the Tigris; their general Chosrhoes swam down the river and made his hideout in a cave.
A second force, under Avidius Cassius and the III Gallica, moved down the Euphrates, and fought a major battle at Dura.

By the end of the year, Cassius' army had reached the twin metropolises of Mesopotamia: Seleucia on the right bank of the Tigris and Ctesiphon on the left.
Ctesiphon was taken and its royal palace set to flame.
The citizens of Seleucia, still largely Greek (the city had been commissioned and settled as a capital of the Seleucid empire, one of Alexander the Great's successor kingdoms), opened its gates to the invaders.
The city got sacked nonetheless, leaving a black mark on Lucius' reputation.
Excuses were sought, or invented: the official version had it that the Seleucids broke faith first.
Whatever the case, the sacking marks a particularly destructive chapter in Seleucia's long decline.

Cassius' army, although suffering from a shortage of supplies and the effects of a plague contracted in Seleucia, made it back to Roman territory safely.
Iunius Maximus, a young tribunus laticlavius serving in III Gallica under Cassius, took the news of the victory to Rome.
Maximus received a generous cash bounty (dona) for bringing the good news, and immediate promotion to the quaestorship.
Lucius took the title Parthicus Maximus, and he and Marcus were hailed as imperatores again, earning the title 'imp.
III'.
Cassius' army returned to the field in 166, crossing over the Tigris into Media.
Lucius took the title 'Medicus', and the emperors were again hailed as imperatores, becoming 'imp.
IV' in imperial titulature.
Marcus took the Parthicus Maximus now, after another tactful delay.

Most of the credit for the war's success must be ascribed to subordinate generals.
The forces that advanced on Osroene were led by M. Claudius Fronto, an Asian provincial of Greek descent who had led I Minervia in Armenia under Priscus.
He was probably the first senator in his family.
Fronto was consul for 165, probably in honor of the capture of Edessa.
P. Martius Verus had led V Macedonica to the front, and also served under Priscus.
Martius Verus was a westerner, whose patria was perhaps Tolosa in Gallia Narbonensis.

The most prominent general, however, was C. Avidius Cassius, commander of III Gallica, one of the Syrian legions.
Cassius was a young senator of low birth from the north Syrian town of Cyrrhus.
His father, Heliodorus, had not been a senator, but was nonetheless a man of some standing: he had been Hadrian's ab epistulis, followed the emperor on his travels, and was prefect of Egypt at the end of Hadrian's reign.
Cassius also, with no small sense of self-worth, claimed descent from the Seleucid kings.
Cassius and Martius Verus, still probably in their mid-thirties, took the consulships for 166.

Vologases IV of Parthia (147–191) made peace but was forced to cede western Mesopotamia to the Romans.
Lucius is reported to have been an excellent commander, without fear of delegating military tasks to more competent generals.
In 165, Roman forces, perhaps led by Martius Verus and the V Macedonica, moved on Mesopotamia. Edessa was re-occupied, Mannus re-installed. His coinage resumed, too: 'Ma'nu the king' (Syriac: M'NW MLK') or Antonine dynasts on the obverse, and 'King Mannos, friend of Romans' (Greek: Basileus Mannos Philorōmaios) on the reverse. The Parthians retreated to Nisibis, but this too was besieged and captured. The Parthian army dispersed in the Tigris; their general Chosrhoes swam down the river and made his hideout in a cave. A second force, under Avidius Cassius and the III Gallica, moved down the Euphrates, and fought a major battle at Dura.
By the end of the year, Cassius' army had reached the twin metropolises of Mesopotamia: Seleucia on the right bank of the Tigris and Ctesiphon on the left. Ctesiphon was taken and its royal palace set to flame. The citizens of Seleucia, still largely Greek (the city had been commissioned and settled as a capital of the Seleucid empire, one of Alexander the Great's successor kingdoms), opened its gates to the invaders. The city got sacked nonetheless, leaving a black mark on Lucius' reputation. Excuses were sought, or invented: the official version had it that the Seleucids broke faith first. Whatever the case, the sacking marks a particularly destructive chapter in Seleucia's long decline.
Cassius' army, although suffering from a shortage of supplies and the effects of a plague contracted in Seleucia, made it back to Roman territory safely. Iunius Maximus, a young tribunus laticlavius serving in III Gallica under Cassius, took the news of the victory to Rome. Maximus received a generous cash bounty (dona) for bringing the good news, and immediate promotion to the quaestorship. Lucius took the title Parthicus Maximus, and he and Marcus were hailed as imperatores again, earning the title 'imp. III'. Cassius' army returned to the field in 166, crossing over the Tigris into Media. Lucius took the title 'Medicus', and the emperors were again hailed as imperatores, becoming 'imp. IV' in imperial titulature. Marcus took the Parthicus Maximus now, after another tactful delay.
Most of the credit for the war's success must be ascribed to subordinate generals. The forces that advanced on Osroene were led by M. Claudius Fronto, an Asian provincial of Greek descent who had led I Minervia in Armenia under Priscus. He was probably the first senator in his family. Fronto was consul for 165, probably in honor of the capture of Edessa. P. Martius Verus had led V Macedonica to the front, and also served under Priscus. Martius Verus was a westerner, whose patria was perhaps Tolosa in Gallia Narbonensis.
The most prominent general, however, was C. Avidius Cassius, commander of III Gallica, one of the Syrian legions. Cassius was a young senator of low birth from the north Syrian town of Cyrrhus. His father, Heliodorus, had not been a senator, but was nonetheless a man of some standing: he had been Hadrian's ab epistulis, followed the emperor on his travels, and was prefect of Egypt at the end of Hadrian's reign. Cassius also, with no small sense of self-worth, claimed descent from the Seleucid kings. Cassius and Martius Verus, still probably in their mid-thirties, took the consulships for 166.
Vologases IV of Parthia (147–191) made peace but was forced to cede western Mesopotamia to the Romans. Lucius is reported to have been an excellent commander, without fear of delegating military tasks to more competent generals.
Lucius Verus