Marcus Aurelius and Lucius Verus Become Co-Emperors

Context

The Roman Empire in the mid-second century operated under the adoptive succession system established by the Five Good Emperors, beginning with Nerva and continuing through Trajan, Hadrian, and Antoninus Pius. This approach prioritized capable administrators over direct bloodlines and contributed to a period of relative stability known as the Pax Romana. Hadrian had arranged for Antoninus Pius to adopt both Marcus Annius Verus and Lucius Ceionius Commodus as heirs, ensuring continuity after Antoninus’s own long reign from 138 onward.

What Happened

Antoninus Pius died on March 7, 161. Marcus, already holding the title of Caesar and favored by the Senate and the army, was immediately recognized as emperor. Out of respect for Hadrian’s earlier wishes and his own sense of fraternal duty, Marcus insisted that Lucius Verus—his adoptive brother—receive equal status as co-emperor, complete with the titles Augustus and Caesar. The Senate ratified the arrangement the same day, marking the first formal instance of two men holding supreme power simultaneously. Marcus retained the title of pontifex maximus, but both men exercised full imperial authority.

Aftermath

The co-emperors quickly divided responsibilities amid rising external pressures. Lucius Verus departed for the eastern frontier in 162 to confront Parthian incursions in Armenia and Mesopotamia, while Marcus remained in Rome to oversee administration and legal affairs. Verus’s campaign concluded successfully by 166 with a joint triumph in Rome, though the returning army brought the Antonine Plague. Lucius Verus died in 169, likely from the plague, leaving Marcus to govern alone.

Legacy

The precedent of shared rule influenced later Roman experiments with multiple emperors during crises, foreshadowing the Tetrarchy of Diocletian. Marcus Aurelius’s philosophical reflections, later published as the Meditations, were composed largely during the joint reign and subsequent wars; they preserved Stoic principles that continued to shape Western ideas of duty, resilience, and rational governance long after the empire’s fall.