As a young boy, Arminius/Hermann/Irmin was given up by his father, a Cherusci chieftain, to the Romans as a hostage to seal a treaty. The young Arminius did so well in Rome that he was granted Roman citizenship, made a noble, and attained military rank. When he returned to his native homeland he did so as a commanding officer with the Roman Legions. However, he witnessed gross infractions by the Romans against his fellow Cheruscians. Secretly, he united several of the Germanic tribes while at the same time convincing Varus, the Roman military leader and his boss, that there was a rebellion about to start. Arminius also convinced Varus that his line of march should pass through the Teutoburg Forest (Teutoburger Wald). The Roman Legions were expert tacticians when it came to waging war on open plains. Teutoburg Forest took that advantage away. Once the Romans were well within the forest, Arminius led his united tribes and annihilated three Roman legions plus their auxiliary units. This battle was Rome's worst military defeat and became known as "Caesar's Nightmare - Varus! Give me back my Legions!" It also ended Rome's expansion east of the Rhine river.
Below are three videos that comprise one of the TLC's series, Archaeology, episodes. This one is titled Caesar's Nightmare: Battle in the Forest 9 CE and is narrated by actor, John Rhys-Davies. You too, may take issue, as I do, to the word Barbarians. I do not fault Davies; it was the script he was given to follow. In concerns about "barbarians," I side with Rudgley (Barbarians, Rudgley, Richard,copyright 2014, Arktos Media Ltd.). The videos are worth watching.
