d previously married to his daughter, and took him as an associate in
the government. Upon the death of Antoninus in March, 161 A. D., Aurelius
succeeded to the principate.

*The dual principate--Marcus Aurelius, 161-180 A. D., and Lucius Verus,
161-169.* Marcus Aurelius at once took as associate in the principate his
adoptive brother, Lucius Verus, and for the first time two Augusti shared
the _imperium_. But the real power rested in the hands of Aurelius, for
Verus was a weak character, indolent and sensual. Although he did not take
the oath not to put a senator to death, and restored the _consulares
iuridici_ removed by Antoninus, the elder Augustus respected the Senate
and remained on good terms with it. Marcus Aurelius was by nature a
student and philosopher, a devoted follower of the Stoic rule of life; his
_Meditations_ bear testimony to the true nobility of his character. Such
was the princeps who was fated to spend his remaining years in an
unceasing struggle against the enemies of the state and, true to his
principles, he obeyed the call of duty and devoted himself unsparingly to
the public service.

*Parthian war: 161-65 A. D.* Even before the death of Antoninus, Vologases
III of Parthia had begun hostilities and had overrun Armenia. The Roman
legate of Cappadocia was defeated and the Parthians broke into Syria,
where they won another victory. The situation was critical. Aurelius sent
his colleague Verus to the scene, and although the latter displayed
neither energy nor capacity, his able generals restored the fortunes of
the Roman arms. In 163 Statius Priscus reestablished Roman authority over
Armenia and placed a Roman vassal on the throne. In 164-65, Avidius
Cassius invaded Mesopotamia and took the Parthian capitals Seleucia and
Ctesiphon. Yet, on the march back, he suffered considerable losses from
hunger and disease, and a peace was made with Parthia which gave the
Romans territory in upper Mesopotamia to the east of the Euphrates (166
A. D.). But the returning troops brought with them a plague which ravaged
the whole empire and caused widespread depopulation.

*Wars with the Marcomanni, Quadi and Iazyges: 167-175 A. D.* In the
meantime a dangerous situation had arisen on the Danubian frontier, where,
probably in consequence of the pressure of migratory peoples, the
Marcomanni, Quadi and the Sarmatian Iazyges united in an attempt to force
their way into the Roman provinces. The army of the Danube had be