Legions I Minervia and V Macedonica, under the legates M. Claudius Fronto and P. Martius Verus, served under Statius Priscus in Armenia, earning success for Roman arms during the campaign season of 163,ᵖ¹⁶³ including the capture of the Armenian capital Artaxata.
At the end of the year, Verus took the title Armeniacus, despite having never seen combat; Marcus declined to accept the title until the following year.
When Lucius was hailed as imperator again, however, Marcus did not hesitate to take the Imperator II with him.
The army of Syria was reinforced by II Adiutrix and Danubian legions under X Gemina's legate Geminius Marcianus.ᵖ¹⁶²
Occupied Armenia was reconstructed on Roman terms.
A new king was installed: a Roman senator of consular rank and Arsacid descent, C. Iulius Sohaemus.
He may not even have been crowned in Armenia; the ceremony may have taken place in Antioch, or even Ephesus.ᵖ²⁸⁰ⁿ Sohaemus was hailed on the imperial coinage of 164 under the legend Rex armeniis Datus: Verus sat on a throne with his staff while Sohamenus stood before him, saluting the emperor.

In 163, while Statius Priscus was occupied in Armenia, the Parthians invaded Osroene, a Roman client state in upper Mesopotamia, just east of Syria, with its capital at Edessa.
They deposed the country's leader, Mannus, and replaced him with their own nominee, who would remain in office until 165.p130, 279 In response, Roman forces were moved downstream, to cross the Euphrates at a more southerly point.
The Parthians still held the southern, Roman bank of the Euphrates (in Syria) as late as 163.
Before the end of the year, however, Roman forces had moved north to occupy Dausara and Nicephorium on the northern, Parthian bank.
Soon after the conquest of the north bank of the Euphrates, other Roman forces moved on Osroene from Armenia, taking Anthemusia, a town south-west of Edessa.
There was little movement in 164; most of the year was spent on preparations for a renewed assault on Parthian territory.ᵖ¹³¹
In 165, Roman forces, perhaps led by Martius Verus and the V Macedonica, moved on Mesopotamia.
Edessa was re-occupied, Mannus re-installed.ᵖ¹⁶⁹ 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.ᵖ¹⁶³
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.p163/4
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 tribune serving in III Gallica under Cassius, took the news of the victory to Rome.
Maximus received a generous cash bounty for bringing the good news, and immediate promotion to the quaestorship.ᵖ¹⁶⁴ 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 Medea.
Lucius took the title 'Medicus', and the emperors were again hailed as imperatores, becoming 'imp.
IV' in imperial titulature.
Marcus took the Parthi
Legions I Minervia and V Macedonica, under the legates M. Claudius Fronto and P. Martius Verus, served under Statius Priscus in Armenia, earning success for Roman arms during the campaign season of 163,ᵖ¹⁶³ including the capture of the Armenian capital Artaxata. At the end of the year, Verus took the title Armeniacus, despite having never seen combat; Marcus declined to accept the title until the following year. When Lucius was hailed as imperator again, however, Marcus did not hesitate to take the Imperator II with him. The army of Syria was reinforced by II Adiutrix and Danubian legions under X Gemina's legate Geminius Marcianus.ᵖ¹⁶²
Occupied Armenia was reconstructed on Roman terms. A new king was installed: a Roman senator of consular rank and Arsacid descent, C. Iulius Sohaemus. He may not even have been crowned in Armenia; the ceremony may have taken place in Antioch, or even Ephesus.ᵖ²⁸⁰ⁿ Sohaemus was hailed on the imperial coinage of 164 under the legend Rex armeniis Datus: Verus sat on a throne with his staff while Sohamenus stood before him, saluting the emperor.
In 163, while Statius Priscus was occupied in Armenia, the Parthians invaded Osroene, a Roman client state in upper Mesopotamia, just east of Syria, with its capital at Edessa. They deposed the country's leader, Mannus, and replaced him with their own nominee, who would remain in office until 165.p130, 279 In response, Roman forces were moved downstream, to cross the Euphrates at a more southerly point. The Parthians still held the southern, Roman bank of the Euphrates (in Syria) as late as 163. Before the end of the year, however, Roman forces had moved north to occupy Dausara and Nicephorium on the northern, Parthian bank. Soon after the conquest of the north bank of the Euphrates, other Roman forces moved on Osroene from Armenia, taking Anthemusia, a town south-west of Edessa. There was little movement in 164; most of the year was spent on preparations for a renewed assault on Parthian territory.ᵖ¹³¹
In 165, Roman forces, perhaps led by Martius Verus and the V Macedonica, moved on Mesopotamia. Edessa was re-occupied, Mannus re-installed.ᵖ¹⁶⁹ 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.ᵖ¹⁶³
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.p163/4
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 tribune serving in III Gallica under Cassius, took the news of the victory to Rome. Maximus received a generous cash bounty for bringing the good news, and immediate promotion to the quaestorship.ᵖ¹⁶⁴ 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 Medea. Lucius took the title 'Medicus', and the emperors were again hailed as imperatores, becoming 'imp. IV' in imperial titulature. Marcus took the Parthi
Lucius Verus