- Aug 2018
First, you have to get rid of the idea that they were "naked savages". Germanics sew linen clothes, and even some were praised by the Romans for their quality. They also possessed basic armour like any other European people. The term "barbarian" in fact is nothing but unreasonable and idiotic Greco-Roman prejudice that is refuted by archaeology and even the Romans' own sources. Some Germanic warriors did fight naked, but they did so for religious reasons, not because Germanics were primitive naked cavemen.Both!
Now, why did Germanics win at Teutoburg Forest? One reason is that Arminius studied Roman tactics. Another is that the Hercynian forest, the forest that basically cut Gaul from Germania and extended deep into the latter, allowed for perfect ambushes. Then there's the fact that Germanics, having basic metallurgy and centuries of warfare (in fact, Germanics inflicted the worst defeat on the Romans based on numbers alone at the Battle of Arausio up to that point, read about the Cimbri and Teutonic invasion from Denmark that was as destructive as Hannibal) could match the Romans. Generally, Romans did not outmatch opponents due to technology but due to organisation and discipline, and that's what gave them the edge over smaller "barbarian" states which did not have the capacity to train a standing army with the same level of discipline.
As to why Germanics, this has been debated a lot. In my personal opinion, it is because Germanics developed shipbuilding comparable to the Romans. The Goths and Heruli were the first non-Roman people during the imperial Pax Romana period to enter the Mediterranean after centuries of piracy had ended. They conquered the Bosphorus and surrounding parts of the Black Sea and launched sea raids similar to the ones by the Vikings. They destroyed the famous Temple of Ephesian Artemis (which also served as a treasury) during one of those raids and also devastated Athens. One Gothic leader called Naulobatus had to be given a high ranking class after his sea raid got deep into the Balkans. It was also part of what allowed the Goths to conquer Dacia, the first Roman province the Romans abandoned.
Not only that, but I suspect that sea raids also gave them an edge over the rival Alans and Sarmatians (Scythians) whom they subjugated, especially with Ermanaric (the greatest emperor you've never heard off; such was his standing among Germanic nations that the Norse of the Viking era were still writing sagas of him), even though the sources aren't clear cut on this. I've always wondered why when the Huns displaced the peoples of the Black Sea we hear only of Gothic leaders but never of Scythian ones (we know that Alans and Sarmatians were with the Goths, but their rulers such as Athanaric and Fritigern are always Goths or have Gothic names at least).
In any case, Germanics were always the ones who inflicted the most devastation on Rome alongside the Celts (here including Hannibal since most of Hannibal's army was made of Celts, or at least a good portion of it). No other people managed to get as deep into Italy as the Teutons and Marcomanni, and they were the first people to also slay a Roman emperor in battle. Part of this may simply be geographic. The Germanics were closer than other people to the Romans, though the Celts were even closer and Romans still overwhelmed most of them. Not to mention that Germanics overwhelmed the Celts. I don't think Caesar would have conquered Gaul without Ariovistus, a Germanic conqueror, invading and devastating it.