I do believe Petraites has a good point here, and it may well be that the Romans were aiming for the Elbe. It makes more sense than the long difficult to defend frontier of the Rhine. At least looking at a map it would seem so not being fullt familiar with the terrain I can not say positively however.

As to Varus' blunder being the beginning of the decline of Rome. No, Rome still had several years of glory in her left. Great Britain, Dacia, and other areas were yet to be sunjugated. Indeed, the Empire did not even reach its greatest extant until Trajan was emperor about 100 years later. IMO, and this is just my opinion, an empire in decline would not have experienced such growth.

What I do feel the Varus disaster indicated though is that Rome was not prepared to deal with the terrain or weather of Northern Europe. Until then, most of their conquests had been in relatively temperate climes. Even northern Gaul was not too bad. The Rhine however did mark a change in both terrain and weather patterns. We are even told by the Roman accounts that Varus had the problem of rains slowing his progress to the benefit of the Germanic tribesmen doing their hit and run raids. By the time Rome had learned to deal with such extreme weather conditions, it was using that knowledge elsewhere such as in Dacia. Too, I have often wondered, if perhaps Rome's own arrogance played a role in not going beyond the Rhine after Varus in any serious way. They conquered Dacia as they considered its existance a threat. It was an organised political entity, in essence, a civilization. The Germanic tribes were not civilized in the Roman sense, they had no cities, were not united politicly, and therefore, Rome may have felt it could conquer the area east of the Rhine at any time. Then Rome simply kept putting off that "any time" as more important issues came up such as the revolt in Palestine, the Dacians, and so forth. Just my opinion.