Marcus Aurelius on the Danube: the opening campaigns, 166–168
In late 166 CE, a Langobardi–Obii raid across the Danube was crushed by Roman forces, prompting envoys led by Ballomar to sue for peace. In 168, Marcus Aurelius and Lucius Verus advanced to Aquileia, raising emergency levies amid the Antonine plague to prepare for a protracted Germanic and Marcomannic war.
The Marcomannic Wars opened with a sharp test of Rome’s Danube line. Cassius Dio dates the first breach to late 166, when six thousand Langobardi and Obii crossed the Ister and were routed by Roman cavalry under Vindex and infantry under Candidus. Alarmed tribes then sought terms through the Pannonian governor, Iallius Bassus, with Ballomar of the Marcomanni among the envoys. Two years later both emperors moved in person to Aquileia, where many kings withdrew, while Marcus shored up Italy and Illyricum, levied volunteers and even gladiators, and hired German auxiliaries. All unfolded under the Antonine plague, which bled manpower and turned frontier policing into continental war.
Key Factors
Antonine plague and manpower shock
From 165 onward, a severe epidemic thinned the ranks, forcing Marcus to improvise. The Historia Augusta notes thousands lost to pestilence, while Galen’s recall during an Aquileian outbreak underscores the strain on logistics and medical care.
Tribal pressure and Ballomar’s diplomacy
Dio’s 166 incursion by Langobardi and Obii triggered wider anxiety north of the Danube. Seeking to avoid immediate escalation, trans-Danubian leaders—led by Ballomar—approached Iallius Bassus to swear peace and pull back.
Redeployment after the Parthian war
With eastern forces returning and units depleted, Marcus raised volunteers, enlisted gladiators, and purchased German auxiliaries to stabilize the frontier. These stopgap measures bought time to refit legions for a larger war.
Aquileia as imperial staging hub (168)
Marcus and Verus marched north in military cloaks, concentrating at Aquileia to harden Italy and Illyricum. Their presence induced some tribal leaders to withdraw and turned Aquileia into the nerve center for the coming campaigns.
Historical Evidence
"“Six thousand Langobardi and Obii crossed the Ister… [and] were completely routed.”"
"“They sent envoys to Iallius Bassus… choosing Ballomarius, king of the Marcomani.”"
"“Both emperors, in military cloaks, set out… they came as far as Aquileia… many kings withdrew with their peoples.”"
"Galen was recalled to Italy in 168–169 and witnessed a winter outbreak near Aquileia."
Part of Marcomannic Wars Begin
This entry anchors the Marcomannic Wars Begin (166) with firm dates, commanders, and the plague’s impact, showing how a border raid escalated into sustained war. It links directly to the Roman Germanic Wars timeline, setting up later crises (170–175) and Marcus’s Germanic and Sarmatian campaigns.
More Questions About Marcomannic Wars Begin
Why did the Marcomannic Wars begin in 166 CE?
A Danube crossing by 6,000 Langobardi and Obii in late 166 CE triggered the Marcomannic Wars. Repulsed by Roman detachments, the raid snowballed into a wider Marcomanni–Quadi–Sarmatian coalition just as Rome’s frontier was weakened by troop redeployments from the Parthian War and the onset of the Antonine Plague.
Marcomanni, Quadi, and Iazyges: Rome’s opponents at the outbreak
The Marcomannic Wars opened in 166–167 with the Marcomanni under King Ballomarius (Ballomar), the Quadi, and the Sarmatian Iazyges launching Danube incursions. Allied groups like the Langobardi and Obii joined, but early crossings were repelled by Roman commanders Vindex and Candidus before Ballomarius led a peace embassy to the Pannonian governor M. Iallius Bassus.
Winter warfare on the Danube: crossings and fortified camps in 166–168
Between 166 and 168 CE, Rome fought a winter defensive war on the mid-Danube, repelling small crossings and consolidating fortified winter quarters at Carnuntum. Marcus Aurelius used Pannonia as his base, restricted frontier markets, and in 168 with Lucius Verus secured Italy and Illyricum—stabilizing the line before later river offensives.
How did the Antonine Plague set the stage for the Marcomannic Wars?
By crippling Rome’s manpower and finances just as Germanic and Sarmatian groups crossed the Danube, the Antonine Plague turned a frontier breach into a protracted war. Contemporary writers record depleted legions, delays at the capital, and emergency sales of imperial treasures—conditions that framed the Marcomannic Wars from 166.