Emperor Huan dies in 168 without a…

Marcus Aurelius makes the Dacian provinces a single military region in about 168.

The limits of Roman territory are probably never clearly defined, but the Romans have benefited both militarily and materially from the occupation.

Marcus Aurelius, like many emperors, spends most of his time addressing matters of law such as petitions and hearing disputes.

Marcus takes great care in the theory and practice of legislation.

He shows marked interest in three areas of the law: the manumission of slaves, the guardianship of orphans and minors, and the choice of city councilors (decuriones).

He revalues the denarius in 168, increasing the silver purity from seventy-nine percent to eighty-two percent—the actual silver weight increasing from 2.57 grams to 2.67 grams.

Marcus and Lucius Verus set forth from Rome in the spring of 168; …

…the coemperors establish their headquarters at Aquileia.

Supervising a reorganization of the defenses of Italy and the Illyricum, Marcus and Lucius raise two new legions, Legio II Italica and Legio III Italica, and cross the Alps into Pannonia.

The Marcomanni and the Victohali have crossed the Danube into the province, but, at least according to the Historia Augusta, the approach of the imperial army to Carnuntum is apparently sufficient to persuade them to withdraw and offer assurances of good conduct.

Historian William McNeill will assert that the Antonine Plague and the later Plague of Cyprian (251–ca. 270) were outbreaks of two different diseases, one of smallpox and one of measles, not necessarily in that order.

he severe devastation to the European population from the two plagues may indicate that people had no previous exposure to either disease, which brought immunity to survivors.

Other historians believe that both outbreaks involved smallpox.

The latter view is bolstered by molecular estimates that place the evolution of measles sometime after CE 500.

The Greek physician and writer Galen had traveled from Rome to his home in Asia Minor in 166, during the epidemic, and returns to Rome in 168 when summoned by the two Augusti—the co-emperors Marcus Aurelius and Lucius Verus; he is present at the outbreak among troops stationed at Aquiléia in the winter of 168/69.

Galen briefly records observations and a description of the epidemic in the treatise Methodus Medendi, and his other references to it are scattered among his voluminous writings.

He describes the plague as "great" and of long duration and mentions fever, diarrhea, and pharyngitis, as well as a skin eruption, sometimes dry and sometimes pustular, appearing on the ninth day of the illness.

The information provided by Galen does not clearly define the nature of the disease, but scholars have generally preferred to diagnose it as smallpox.

Emperor Ling, after the destruction of the Dou clan, honors his mother Consort Dong as an empress dowager in 169, but continues to also honor Empress Dowager Dou (now placed under house arrest by the eunuchs) as an empress dowager.

Members of the Dong clan begin to enter government, but do not have substantial influence.

Later this year, the eunuchs persuade Emperor Ling that the "partisans" (i.e., Confucian officials and Academy students who support them) are plotting against him, and a large number of partisans are arrested and killed; the others have their civil liberties stripped completely, in what later is known as the second Disaster of Partisan Prohibitions.

Marcus sets out from Rome in the autumn of 169, together with his son-in-law Claudius Pompeianus, who will become his closest aide during the war.

The Romans have gathered their forces and intend to subdue the independent tribes (especially the Iazyges), who live between the Danube and the Roman province of Dacia.

The two emperors return to Aquileia for the winter, but Lucius Verus dies on the way, in January 169.

Marcus returns to Rome to oversee his co-emperor's funeral.

The Iazyges defeat and kill Marcus Claudius Fronto, Roman governor of Lower Moesia, in 170.

Operating from Sirmium (today Sremska Mitrovica, Vojvodina, Serbia) on the Sava river, Marcus Aurelius moves against the Iazyges personally.

After hard fighting, the Iazyges are pressed to their limits.

However, while the Roman army is entangled in this campaign, making little headway, several tribes use the opportunity to cross the frontier and raid Roman territory.

The Costoboci cross the Danube, ravage Thrace and descend the Balkans.