The Teutoberg forest is just one example.They won thatbattle simply becuase of their fighting skills.The Romans were excellant fighter in OPEN battle and thier formations but in the Forest with more enclosed fighting and more personal skils needed they were wiped out by the tribes of northwest Europe.
Please. No it wasn't, it was simply treachery on part of Arminius. The Romans were not marching in a disciplined formation, marching w/o wearing armor, unprepared for any attack simply because Arminius was supposed to be a Roman ally but was in reality a treacherous enemy. The battle was simply a German ambush/massacre of unsuspecting, unready to fight Roman soldiers.
Today’s equivalent would be if a few battalions of German Leopard 2s rolled up to Wiesbaden Airfield and started blasting away at US troops.