Teutoburger Wald. Right.
Followed by a couple of decades of Roman armies stomping all over Germany in reprisal.
http://en.wikipedia.org/wiki/Germanicus
The Roman Empire had a natural boundary at the Sahara and Atlantic. In Germany, Scotland and Syria they had to define a border, or keep expanding forever. No natural boundaries.
The Empire decided, quite rightly IMO, that the effort of conquering and occupying Germany was not worth the gain. Obviously, if Germany had been occupied and assimilated, there would simply have been another border with barbarian tribes on the other side, just farther away from the Roman heartland and therefore even harder to defend effectively.
The Romans eventually decided to defend the line of the Rhine and Danube, which seems as logical as any.
This dilemma of where to place the border is similar to that of Israel today. Some call for Israel to conquer and annex land because attacks are launched on Israel from that land. But of course there will still be attacks launched from the land beyond the new borders. So unless one can reach a natural border, there is no logical stopping point.
Despite the defeat in 9 AD, the Romans successfully defended the frontier for more than 300 years thereafter. The various incursions by German tribes, all repelled eventually, were all related more to internal Roman difficulties. Civil wars and such, which were endemic.
As Roman defeats go, Teutoburger Wald was really fairly minor as far as losses go.
Cannae, for instance, resulted in 2x to 4x the number of dead Romans, at a time when the resources of the Roman State were MUCH smaller. IOW, something like 75% of the Roman Army, not 10%.
Teutoburger Wald was strategically important because it eventually convinced the Romans not to expand farther into northern Europe. But it was a Roman loss, not a German victory, since the Germans never even tried to invade and conquer Rome, whereas the Germans spent most of the next couple of decades running away and hiding from Roman armies.
“But it was a Roman loss, not a German victory, since the Germans never even tried to invade and conquer Rome, whereas the Germans spent most of the next couple of decades running away and hiding from Roman armies.”
Germans eventually DID sack Rome (as did Celts); Germans had no reason to hide from an aggressor that, as in Scotland, huddled behind defenses and bribed their way out of defeat for centuries as they died a slow death. There are a lot more Germanic people in northern Italy today than Italians in southern Germany.