How does the Western Empire do with an Elbe-Danube frontier?

[FrozenMix]

As it was stated above, most of western and southern Germania was celtized and close to what existed in Gaul.

Giving that Rome managed to export a lot of its feature and way of life trough trade and clientelism in Gaul (It's particularly obvious in the last century of independent Gaul, with decline of druidism, rise of vergobret, the lot of roman coinage and roman products), I don't see why it couldn't be done as well in these regions.

In a previous thread about Caesar failing to takeover Gaul, I suggested that a surviving Ariovist's confederacy, allied with Rome, and crossing Rhine to dominate Sequani and southern Germanic (in the geographical meaning) peoples, and *maybe* Helvetii, could form a strong entity comparable to which influence Aedui had in Central Gaul.
Such entities, with a following conquest/absorbtion, could be a good first step for what you search.

There is definitely evidence suggesting that Germania in the 200s AD was vastly more conducive to being conquered and integrated into the Empire than it was when Rome actually was trying to do so in the reign of Augustus. Contact with Rome had definitely affected them, as you said regarding western and southern Germania.

I guess I was referring to if Rome decided to make another go at it after Teutoberg and really went for it rather than just avenging honor and punishing the tribes. That kind of war would be really nasty from start to finish, and likely would reflect the Cantabrian Wars rather than the Gallic campaigns.

The political will and stability to do this however is a lot more difficult to find than the military ability to carry it out. I suggested Severus's reign maybe being the time for it, and maybe, one of the five Good Emperors could have given it a go, but it likely would have been a more difficult conquest at that point.

I suppose that you are right that in time, the ability for Romanization to occur increases, but the window for the military and political determination to get this done decreases.

 

[LSCatilina]

I suppose that you are right that in time, the ability for Romanization to occur increases, but the window for the military and political determination to get this done decreases.

That's a fair and sound point, and as a slower and more gradual conquest of Gaul (to preserve as much as possible social-economical structures with South Germania) would take time and the aformentioned window would be greatly reduced.
On this, I don't claim having an answer, just pointing that any choice would have downsides.

 

[Lewx]

What does the Eurasian plain have to do with the Elbe? It's hardly much closer to it than the Rhine. Dacia and the Danube frontier are under greater threat from the steppes than Northern Germany.

http://geopoliticsmadesuper.com/201...politics-and-why-it-wanted-out-to-begin-with/

"
Germany’s resource base and climate make it a great place to rule. It’s relatively mild climate allows a good growing season; its storied forests provide plenty of timber; its hills and valleys provide coal, uranium, natural gas, and iron. It has all the resources necessary to industrialize on the cheap and build a huge manufacturing base that outclasses most of its neighbors.
On three sides, Germany has defensible borders. To the north is the Baltic Sea, a tough proposition to cross, especially in winter. To the west is the Rhine, an easily-fortified river system that also gives German businesses quick access to the ocean. And to the south are the mighty Alps. Few conquerors have ever come from those three sides.
Germany as a historical concept goes all the way back to the Classical Age. When the Romans decided where to draw their military frontier, they followed Germany’s natural frontiers: the Rhine and the Alps. Even though Roman power could have conquered Germany as we know it today, they didn’t. Why?


Because of the (applause, please!) Great Northern European Plain

Had the Romans decided to occupy Germania, they would have faced an open sea of grass and forest that stretches all the way to Mongolia. Teeming with nomadic tribes, many of them well-armed, the Romans would have found themselves in an endless and exhausting series of campaigns pushing that frontier further and further east, trying to find a frontier that could be held long-term. The Romans knew better; they drew the line at the Rhine and the Alps and preferred to contain Germany rather than take on the liability of its eastern, open frontier."


The Romans were smart enough to not repeat Alexander's mistake. Alexander depleted his capacity on trying to establish security by conquering everything. Rome preferred to set up buffer states where it was possible.


Alexander was smarter than Hitler, whose entire goal was to march to the Urals (which pretty much are hills anyway, not mountains).

 

[HunterX]

Classifying Germania of antiquity near the Elbe as part of the Eurasian steppes is quite strange.

 

[GdwnsnHo]

<snip>

I'm not a fan of that article, mainly because whilst I do acknowledge the importants of natural borders, it smacks a bit too much of Geographical Determinism for my taste.

Mainly because it whitewashes the nuance out of geographical defensibility. Rivers may be less defensible than mountains, and may be awful as the mountains and rivers have to have a certain quality to make the job easier. For example, the Zagros and Urals aren't particularly good because they are too permeable, or easily avoided - or too difficult to fortify (Even if they make good demographic and psychological borders - don't discount those). Even the Alps, which are a fantastic natural border aren't complete without the fortifications to finish the job of making them a border - and then maintain them, otherwise anyone can "Pull a Hannibal" and cross the Alps (Or Pull a Romans and conquer everyone east and west and immediately north of the alps). Smaller tribes have difficulty with this, and I'd posit that the Germans never did because they had no polity of significant unity, economic strength to do so until the Prussians, and at that point it granted them no advantage.

I'll concede to all that the Elbe is not as easy to defend as the Rhine. Especially after the Rhine was fortified, I just believe the big questions are :-

a) Could the Romans reach the Elbe and hold the territory it delimited.

b) Could the Elbe be made equally defensible, and would the defences and the invasion be worthwhile?

So,

a1) Yes, they historically reached the Elbe, which suggests it could be done in an ATL. It was historically only prevented by largely domestic issues rather than the German territories themselves.
a2) Regarding holding the territory, there are the resources available and the Romans had the infrastructure technology to do so. Rome was famous for its roads, and its use of shipping (though I'm not familiar with its river-based shipping, so that may be a weakness)

b1) Considering the steepness of many of its valleys, I'd say it is largely defensible, with forts that could bombard/engage anyone daring to cross the river. It even has its own river island to fortify as a magnificent centrepiece for a Roman Elbe Military Complex. It probably merits more discussion other than a few topographic maps I've taken a quick look at - so I'd be curious to be proven wrong here. Why did no-one do it historically, I'm sticking with whom controlled the river at any given time. The only polity that would have considered it an border frontier AFAIK would be the Carolingians, but that was difficult to even keep stable, let alone start fortifying its borders!

I'm now mostly curious about how defensible the Elbe is as the only instantly apparent major shortcoming of the Elbe (to me) is that it appears to be narrower for the majority of its length - which is normal for a shorter river. But it does have steep valleys that are defensible on both sides - and when it flattens out, it has the same defensive problems that the Rhine itself would have had in that it is easy to attack the floodplains. I would submit it has a not insurmountable weakness in that it is easier to approach from the East through Poland, than the West through Germany because of the mountains in South and West Germany.

 

[LSCatilina]

Eurgh, obnoxious pop-politics. I feel nauseous reading it all.

Worse than that, it doesn't even contribute anything that hasn't already been said. (Other than history of Germany that exists long after the PoD to reinforce something that we're all already aware of, so thanks for that.)

You know, so far and in spite of many disagreements among the posters in this thread, exchanges were polite and enjoyable.
I certainly not congratulate you for breaking this with something that uncalled for, regardless of agreeing with part of your post especially on geographical determinism.

That said, the absence of strong fortification lines on early medieval Elbe is more due to different conceptions of war and border than political stability : an army was gathered locally or regionally at a given point, the great expeditions being more rare, to act on a border that was considered by essence porous (not only for neighbouring peoples, but for Carolingian and post-Carolingian armies as well) because of (among other factors) the absence of clearly defensible borders (the Limes Saxonicum being essentially a line crossing hard to cross ground, such as forests and bogs).

While it could be a point to Lewx, I don't think it could be applied to Romans that were less reliant on "big natural borders" than generally assumed and with a really different take on strategical distribution.
It's why I think that establishing a series of valli and limes in western Germany (supported by WG fluvial system) could be the most interesting compromise between expansion and domestic issues : doing that would hardly be a technical and infrastructural issue for them.

 

[GdwnsnHo]

You know, so far and in spite of many disagreements among the posters in this thread, exchanges were polite and enjoyable.
I certainly not congratulate you for breaking this with something that uncalled for, regardless of agreeing with part of your post especially on geographical determinism.

Looking back at this I have to admit, it certainly doesn't come across as one of my finer moments - and I'm going to edit that so that people don't need to deal with it, as it certainly doesn't come across as polite - but I will apologise to everyone whom has taken part in the thread and particularly to @Lewx because re-reading that now it does come across more as a sarky personal attack rather than the original intention of condemning the article - which in fairness I should have only critiqued, or just left well alone.

So I'll leave that there as an acknowledgement of my regret - obnoxious an apology as this may be.

That said, the absence of strong fortification lines on early medieval Elbe is more due to different conceptions of war and border than political stability : an army was gathered locally or regionally at a given point, the great expeditions being more rare, to act on a border that was considered by essence porous (not only for neighbouring peoples, but for Carolingian and post-Carolingian armies as well) because of (among other factors) the absence of clearly defensible borders (the Limes Saxonicum being essentially a line crossing hard to cross ground, such as forests and bogs).

I did think I'd covered this with pre-modern warfare, but I hadn't considered the different styles of war - though I'd still be inclined to believe that political stability would play a role in whether or not those great expeditions could take place, or any polity could create the great defences to make a comparatively porous border (think pre-Great Wall China) into an incredible defence, (post-Great Wall China). (I'd mention the names of at least a mountain range, but even the articles on the passes walled up by the project don't mention its name. How very odd). Though I suppose that construction would never take place if none of the contemporaries considered it worthwhile or cost effective, as you (appear) to suggest the Carolingians and their successors thought.

While it could be a point to Lewx, I don't think it could be applied to Romans that were less reliant on "big natural borders" than generally assumed and with a really different take on strategical distribution.
It's why I think that establishing a series of valli and limes in western Germany (supported by WG fluvial system) could be the most interesting compromise between expansion and domestic issues : doing that would hardly be a technical and infrastructural issue for them.

As in a series of Roman "Maginot Lines?" I'm just imagining it in my head and that is the nearest comparison I have, which would suggest that it'd be significantly effective until tanks/people go around it.

 

[LSCatilina]

Though I suppose that construction would never take place if none of the contemporaries considered it worthwhile or cost effective, as you (appear) to suggest the Carolingians and their successors thought.

Well, there's the possibility of partially porous and partially symbolical borders. Offa's Dyke is a good exemple, as the Danevirke but they were more about a defensive protection, "sanctuarizing" (if you allow me the anachronism) a given territory rather than establishing an idealized front line.

(It should be pointed out that both were built by what was described as cyclical chiefdoms, with inherent unstability)

It doesn't mean carolingians didn't established fortifications akin to late Romans : it's just that we don't have much archeological proofs for now. I'd suggest this article, if it interests you.

As in a series of Roman "Maginot Lines?" I'm just imagining it in my head and that is the nearest comparison I have, which would suggest that it'd be significantly effective until tanks/people go around it.

I was more thinking about African and Dacian limes.

I think I may have explained myself badly : I didn't meant a series of parallel fortifications, or ultra-fortifying the same position, but building a territorial expension trough protections that while based on natural features, would be modulable and expendable enough to be abandoned by others when needed.

For example, two limes joining two different points from Danube to two parallel points in the Bohemians highlands. These being only one part of a greater ensemble of valli and defensive structures in Western Germany, allowing in case of crisis to back up to the Rhine without a too great infrastructural expense.

 

[GdwnsnHo]

Well, there's the possibility of partially porous and partially symbolical borders. Offa's Dyke is a good exemple, as the Danevirke but they were more about a defensive protection, "sanctuarizing" (if you allow me the anachronism) a given territory rather than establishing an idealized front line.

(It should be pointed out that both were built by what was described as cyclical chiefdoms, with inherent unstability)

Oooh, both are interesting - I'd never heard of the Danevirke - and the idea that it may have been partially a later-fortified canal is interesting, and would explain why the area would be chosen as a later area to fortify. Though it does seem reminiscent of the pre-Great Wall ... walls, that the Chinese built.

Though the doubt on Offa's Dyke being Mercian is interesting, I do think that it being "unflankable" certainly helps, as does at a glance seem to be a talented Mercian King. The idea of it being late Roman seems more plausible from an administrative perspective, but oddly simple compared to their other fortifications. Though it would have certainly have helped in ensuring Mercian hegemony, and perhaps why they retained control over that border for most of their existence. Not to diminish the achievement though. Perhaps I underestimate smaller polities.

It doesn't mean carolingians didn't established fortifications akin to late Romans : it's just that we don't have much archeological proofs for now. I'd suggest this article, if it interests you.

Yay, because I needed something to read *looks at imposing to read pile - consumes anyway*

I was more thinking about African and Dacian limes.

I am an amateur, so my analysis may be worth bunk, but those Dacian limes look, well ... odd at first glance. Whilst I can get behind the Greuthungian and Antharic walls, the Transalutanus looks at best confusing regarding its purpose and the Constantine limes are in a better position to defend Dacia proper from the Romans than the other way around. Reading into them (So people don't have to wiki - Transalutanus for defending a river, the Constantine Limes and the Devils Dykes to protect tributary tribes) they make more sense. Not my ideal choice as they seem too short-term to really justify serious fortification work.

I think I may have explained myself badly : I didn't meant a series of parallel fortifications, or ultra-fortifying the same position, but building a territorial expension trough protections that while based on natural features, would be modulable and expendable enough to be abandoned by others when needed.

For example, two limes joining two different points from Danube to two parallel points in the Bohemians highlands. These being only one part of a greater ensemble of valli and defensive structures in Western Germany, allowing in case of crisis to back up to the Rhine without a too great infrastructural expense.

I think I understand what you're getting at. I think (what is a valli?). The double Danube-Bohemian limes certainly sounds like it'd be effective if there was a hostile Dacia (or if built the right way, a hostile Germania and docile Dacia).

If I've understood, then those expendable fortifications could work really well for a sort of "Creeping Conquest" of Germania - simpler defences for tributaries, only taking from their neighbours the barest minimum to create a solid defensive line, stabilising and building a fortified city(?) before moving on to the next set of cost-effective defences, repeat the process till the Elbe, then use that as a replacement Rhine, and perhaps have a layer of tribes on the far side too. It'd have the advantages of short-term cost effectiveness, whilst building/reinforcing the economic strength in the area as the borders advance. I can see maybe 7/8 potential really solid defensive lines as you come up through S.Germany for this approach, and the Ems and Weser could help with that too. Though I'd be loathe to leave the Elbe alone once you're so close, as it could be used to hide behind and harass the last layer of fortifications. It does concern me that it could be seen as a drain in Italia, unless the majority of the construction was done by the soldiers. I'd be concerned that a significant chunk of progress could be lost every time there was a civil war however, unless the "Germanic" Legions were remarkably apolitical.

 

[Dathi THorfinnsson]

I think I understand what you're getting at. I think (what is a valli?). The double Danube-Bohemian limes certainly sounds like it'd be effective if there was a hostile Dacia (or if built the right way, a hostile Germania and docile Dacia).

A "vallus" (plural valli) is a palisade. A "vallum" (plural valla) is a series of such, e.g. Hadrian's Wall is a vallum. As is a circumvallation.

 

[Matteo]

http://geopoliticsmadesuper.com/201...politics-and-why-it-wanted-out-to-begin-with/

"
Germany’s resource base and climate make it a great place to rule. It’s relatively mild climate allows a good growing season; its storied forests provide plenty of timber; its hills and valleys provide coal, uranium, natural gas, and iron. It has all the resources necessary to industrialize on the cheap and build a huge manufacturing base that outclasses most of its neighbors.
On three sides, Germany has defensible borders. To the north is the Baltic Sea, a tough proposition to cross, especially in winter. To the west is the Rhine, an easily-fortified river system that also gives German businesses quick access to the ocean. And to the south are the mighty Alps. Few conquerors have ever come from those three sides.
Germany as a historical concept goes all the way back to the Classical Age. When the Romans decided where to draw their military frontier, they followed Germany’s natural frontiers: the Rhine and the Alps. Even though Roman power could have conquered Germany as we know it today, they didn’t. Why?


Because of the (applause, please!) Great Northern European Plain

Had the Romans decided to occupy Germania, they would have faced an open sea of grass and forest that stretches all the way to Mongolia. Teeming with nomadic tribes, many of them well-armed, the Romans would have found themselves in an endless and exhausting series of campaigns pushing that frontier further and further east, trying to find a frontier that could be held long-term. The Romans knew better; they drew the line at the Rhine and the Alps and preferred to contain Germany rather than take on the liability of its eastern, open frontier."


The Romans were smart enough to not repeat Alexander's mistake. Alexander depleted his capacity on trying to establish security by conquering everything. Rome preferred to set up buffer states where it was possible.


Alexander was smarter than Hitler, whose entire goal was to march to the Urals (which pretty much are hills anyway, not mountains).

This is a smart reasoning. However, I will not applause.

The big european rivers (Weser, Elbe, Oder, Vistule) that flow in central and eastern Europe are no more no less natural frontiers than the Rhine and the Danube.

And nobody in Rome knew about the existence of Ural nor about the sea of grass and forest stretching to Mongolia, nonetheless about Mongolia.

They tried several ways of controling Germany west of the Elbe. They finally opted for indirect control and it more or less worked until the great migrations.

 

[Magnum]

To add my 2 cents to the discussion:

I think the main problem for the Romans was not the exact length of the frontier, or whether it as situated on this or that river, or on how exactly the limes was built etc etc., but rather who inhabited the land on the other side of said frontier.

After the end of the civil wars and the establishment of the Principate, Rome was strong enough to make Germania a wasteland and call it peace if it so desired. The problem was that there wasn't anything valuable (that was in plain sight) for them to subjugate - it was deemed much cheaper to establish buffer 'states' and trade with the tribes on the frontier, especially since the societal make-up of said tribes IMHO prevented them from ever being in a position to undertake large-scale campaigns capable of threatening anything of value to Rome.

Centuries of trading with and serving for the Empire eventually transformed said Germanic societies - had the Roman state been in the same shape it was during the previous period, it would probably have found it desirable to subjugate at least part of Germania. The problem was the 3rd Century crisis, which seriously weakened the state, and the rise of Sassanids, which again forced them to devote a substantial part of their ressources to that front. However, the change to Germanic societies also allowed them to organize campaigns that penetrated deep into the Empire as soon as the right moment presented itself.

Therefor, I think that, had the Roman Empire made a committed effort right before the 3rd century crisis (reign of Alexander Severus would have been the ideal moment, as Persia was in a civil war) and incorporated the then much more amneable to romanization Germania, it would have made a huge difference at the time of the Völkerwanderung. Simply put, there would have been no tribes advanced enough to do the kind of damage the Empire endured in the 5th century; any Germanic coalition the Huns would have assembled would have been much weaker and the reduced threat in Germany would have probably allowed the Empire to decisively repel the Goths at Adrianople like they did at Naissus.

By the time the next set of tribes had been changed enough via their contact with Rome, things would have settled down as the Great Migration period would have ended by then, thus providing little incentive for these tribes to actively seek a confrontation with Rome.

 

[Russian]

To add my 2 cents to the discussion:

speaking of two cents...

I am shocked that the Great Illyrian Revolt was mentioned only once in this thread. As this is alpha and omega to the matter of Germania being (un)conquered by the Romans.
And this is not only the immediate effect - the impossibility to reinforce Varrus in Germany or later revenge his inglorious defeat and drown these rebel Germans in their own blood.
I am speaking about long time effect.
First of all we have to realize that the Great Illyrian Revolt is severely underappreciated by our historians. The Romans of the first century AD compared it to the Punic wars.

Actually in my opinion the Romans knew what would happen if they try to conquer Germany as they already had it in miniature in Illyria/Pannonia:

Illyria was ruled by the Romans (mostly directly) good hundred years (some parts even longer) it was considered properly pacified, as (mostly) it was hellenized, romanized country with ancient culture, town life and so on.
But it rebelled given a chance.
No one could predict such ferocious revolt from their part, it was totally unexpected by the Romans meaning the scope and determination.
You cannot avoid thinking about the Gaul (the part which was conquered by Julius Caesar) - it was newly conquered compared to Illyria and may revolt just the same.

So if the Romans start the war of conquest in Germany they might have an all-Gaullic uprising in the Gaul. But the scope the scale of this Great Celtic/German revolt would be 5 times more than in Great Illyrian Revolt. And that "Mother of all the Revolts" would break the backbone of the Roman might.

It is a pity I cannot remember which of the Latin writers said (it was not Suetonius Tranqull I guess, maybe Tacitus) but definitely living in the second half of I century AD:
"the Roman legions on the Rhine are ideally placed - they watch over Germany and at the same time they guarantee that Gaul does not revolt".

My point here is moving these legions into Germany would break this ideal disposition.
I guess the Romans thought: "Let's not spoil this good thing.'

 

[Cambyses]

I think a lot depends on whether this is done around the time of Augustus, that of Septimius Severus or even somehow that of Constantine

Augustan era would probably need a POD changing Varus' fate, as that rather put Augustus off expansionism.

I don't think Severus could have done it, tbh. The losses he sustained (and, indeed, inflicted) against Albinus cost the Empire too much manpower to consider an ambitious conquest. Around that era though, the German Tribes were pretty much exhausted after the Marcomannic wars, so having a competent person succeed Marcus Aurelius could be a workable POD. Pompeianus could be suitable, as if Commodus croaked or was sidelined he would have made a good candidate for adoption, and IIRC he actually wanted to extend the war.

As for the Constantinians, Julian might be a good choice. He was very successful in Germany after all.

 

[Lewx]

I'm not a fan of that article, mainly because whilst I do acknowledge the importants of natural borders, it smacks a bit too much of Geographical Determinism for my taste.

Mainly because it whitewashes the nuance out of geographical defensibility. Rivers may be less defensible than mountains, and may be awful as the mountains and rivers have to have a certain quality to make the job easier. For example, the Zagros and Urals aren't particularly good because they are too permeable, or easily avoided - or too difficult to fortify (Even if they make good demographic and psychological borders - don't discount those). Even the Alps, which are a fantastic natural border aren't complete without the fortifications to finish the job of making them a border - and then maintain them, otherwise anyone can "Pull a Hannibal" and cross the Alps (Or Pull a Romans and conquer everyone east and west and immediately north of the alps). Smaller tribes have difficulty with this, and I'd posit that the Germans never did because they had no polity of significant unity, economic strength to do so until the Prussians, and at that point it granted them no advantage.

I'll concede to all that the Elbe is not as easy to defend as the Rhine. Especially after the Rhine was fortified, I just believe the big questions are :-

a) Could the Romans reach the Elbe and hold the territory it delimited.

b) Could the Elbe be made equally defensible, and would the defences and the invasion be worthwhile?

So,

a1) Yes, they historically reached the Elbe, which suggests it could be done in an ATL. It was historically only prevented by largely domestic issues rather than the German territories themselves.
a2) Regarding holding the territory, there are the resources available and the Romans had the infrastructure technology to do so. Rome was famous for its roads, and its use of shipping (though I'm not familiar with its river-based shipping, so that may be a weakness)

b1) Considering the steepness of many of its valleys, I'd say it is largely defensible, with forts that could bombard/engage anyone daring to cross the river. It even has its own river island to fortify as a magnificent centrepiece for a Roman Elbe Military Complex. It probably merits more discussion other than a few topographic maps I've taken a quick look at - so I'd be curious to be proven wrong here. Why did no-one do it historically, I'm sticking with whom controlled the river at any given time. The only polity that would have considered it an border frontier AFAIK would be the Carolingians, but that was difficult to even keep stable, let alone start fortifying its borders!

I'm now mostly curious about how defensible the Elbe is as the only instantly apparent major shortcoming of the Elbe (to me) is that it appears to be narrower for the majority of its length - which is normal for a shorter river. But it does have steep valleys that are defensible on both sides - and when it flattens out, it has the same defensive problems that the Rhine itself would have had in that it is easy to attack the floodplains. I would submit it has a not insurmountable weakness in that it is easier to approach from the East through Poland, than the West through Germany because of the mountains in South and West Germany.

I am a geographical determinist, at least moderately so.

But no, the cost of Romanization/Extermination of the Germanics, and the defense, was believed by the Romans to be too high. Instead, they preferred to civilise the Germanics by trade, and create client states in the region. It was a successful tactic, and the big problem up until the 400's was not the Rhine but the Danube.

The Romans could have taken Germany to the Elbe anywhen until the 5th century. Even Maximianus defeated the Germans in a big battle in the middle of Germany.

The reason why not is basically the same as why the Americans in the 19th century did not simply cakewalk over Mexico.

 

[Cambyses]

The reason why not is basically the same as why the Americans in the 19th century did not simply cakewalk over Mexico.

But...they did...

 

[GdwnsnHo]

I am a geographical determinist, at least moderately so.

But no, the cost of Romanization/Extermination of the Germanics, and the defense, was believed by the Romans to be too high. Instead, they preferred to civilise the Germanics by trade, and create client states in the region. It was a successful tactic, and the big problem up until the 400's was not the Rhine but the Danube.

The Romans could have taken Germany to the Elbe anywhen until the 5th century. Even Maximianus defeated the Germans in a big battle in the middle of Germany.

The reason why not is basically the same as why the Americans in the 19th century did not simply cakewalk over Mexico.

But they only implemented that policy post-Teutoburg, where that psychological blow totally changed their policy. Prior to that they we quite happy to expand in Germania.

In addition, the Roman Empire proper formed largely out of client states and "allies" that got absorbed into the Empire proper. Not sure what would prevent them doing that in Germania when it was ripe.

 

[Lewx]

But they only implemented that policy post-Teutoburg, where that psychological blow totally changed their policy. Prior to that they we quite happy to expand in Germania.

In addition, the Roman Empire proper formed largely out of client states and "allies" that got absorbed into the Empire proper. Not sure what would prevent them doing that in Germania when it was ripe.

They did not need to. The client states that got absorbed were Mauretania (which was absorbed just because Caligula had messed up the economy), and the many Middle Eastern minors who otherwise were constant sources of tensions with Parthia.

There were no powerful states east of the Elbe until the 5th century. There were lots of tribes however.

Rome would just have had to confront Sarmatians, Venedi and Goths instead of Germanics. And later on they would have found themselves fighting Scythians and Turks.

The only Empire which successfully beat down that entire route east was Russia, and that's because they had no choice.

 

[Russian]

The only Empire which successfully beat down that entire route east was Russia, and that's because they had no choice.

... and had firearms.

 

[LSCatilina]

But they only implemented that policy post-Teutoburg, where that psychological blow totally changed their policy. Prior to that they we quite happy to expand in Germania.

The psychological shock was more exxagerated than really existing. The problem is less that Romans acquired a phobia of Germania, than they really tought they over-streched their forces : the withdrawn on clear borders is far from being only happening on the Rhineland, but is a general feature dictated by inner policies, fear of returning back to the "popular general" trope and all it implied politically, or simply lack of ressources.
It's particularly obvious with Britain, for exemple.

In addition, the Roman Empire proper formed largely out of client states and "allies" that got absorbed into the Empire proper. Not sure what would prevent them doing that in Germania when it was ripe.

The clientelisation/absorbtion was more and more seen as ineffective by Romans in the Ist century. Basically, these revolted too much, were too resistant to political domination, and prooven being generally unreliable.
Hence why Augustus and his successors went trough a series of direct annexations of territories, or annexed client states, said policy culminating with Trajan.

(Also answering previous post that I totally forgot)

Though the doubt on Offa's Dyke being Mercian is interesting, I do think that it being "unflankable" certainly helps, as does at a glance seem to be a talented Mercian King.

To be frank, I always was under the impression that more of the doubts were more based on an unnapreciation of Offa's possibilities, more than clear analysis : now, it's possible that the dyke was built on previous structures, but the whole is, IMHO, the work of Mercians in contact with hostile Cymric entities.
The point of the structure may be not only strategical, even if it certainly had a military utility, than being hugely symbolical, definitely marking Mercian territory in the eyes of Anglo-Saxons and Cymric raiders.

The idea of it being late Roman seems more plausible from an administrative perspective, but oddly simple compared to their other fortifications

Roman limes themselves weren't exactly what we would call continuous fortifications lines, at least not until the late Ist century, but were understood as progression lines, eventually trough ennemy territories, protected by fortifications when needed.
Basically, before Domitian and Hadrian, what characterised the limes was less the fortifications than the roads it protected, and while the fortification took more and more importance with time in the definition.

It's basically what I proposed while talking about Weser and Main fortifications : protection of progression lines, not being huge loss if not being maintainable, but allowing a relativly fast and safe progression deeper in the region. Not a copy of the Agri Decumati that while seen as a protection of the military road between Raethia and Gaul, was a defensive line.