You're looking at what the brilliant stoic, general, elected Roman Consul and (Emperor), Marcus Aurelius fought for and did during his entire term as Consul... he was trying to keep Rome intact. He served during the last Pax-Romana 161 - 180 A.D. which (imo) is why the Germans handled his garrisons with ease (numbers helped as well).
Always wildly outnumbered by the Germanic tribes from the north, Marcus Aurelius had to fight strategic battles spread across vast distances, where he often lost 10's of thousands of men. One front after another, the German tribes were relentless and actually 'scared' Roman soldiers with their loud sounds and their incessant brutal savagery.
The Germanic "barbarians" were fierce warriors who had a "we come and we stay or we die" spirit. Even the women and children would take an axe and split Roman heads... because that's what we did!
Guess where the 'barbarians' got the idea for military formations making them unstoppable? That's right the Romans!
Crazy huh! The Roman Empire ruled all, except one thing, they couldn't break the Germans.