Comment by fsckboy

>This might have been a small detachment that was ambushed and utterly wiped out

or even three legions, 16,000–20,000 killed. "Teutoburg Forest is considered one of the most important defeats in Roman history, bringing the triumphant period of expansion under Augustus to an abrupt end. It dissuaded the Romans from pursuing the conquest of Germania, and so can be considered one of the most important events in European history."

https://en.wikipedia.org/wiki/Battle_of_the_Teutoburg_Forest