One reason these fortresses in Picardy, Flanders, and Batavia did not come into play in the "Napoleonic" wars, was because there were no major campaigns there--other than the Waterloo campaign, which lasted at the most one month. So, of course, we don't hear much about these fortresses in the lowlands from accounts of the day. Napoleon was lucky enough to gain the Netherlands as a minor ally and then annexed it in a series of political maneuvers which I have never found a good source on (anyone out there know a good source on that?)
However, the presence of these fortifications was felt in every war previous to the "Napoleonic Wars" whose area of operations lie within that region. This is one reason why the Netherlands did not fall after repeated assault by Spain and France in the 1500s, 1600s, and 1700s. It is also the reason that there was never a serious advance towards Paris during the war of the Spanish Succession. These frontier regions were solid, virtually water tight, and sported the highest density of first rate fortifications in the world. Indeed, it was Vauban's boast that "every single spot in the barrier zone between Switzerland and the North Sea be within earshot of the cannon of a French garrison." For this, he designed the double defensive lines of that frontier (seen below). Off the eastern end of the lines shown below, the defenses moved into Germany, culminating in one of Vauban's masterworks: Landau.
Napoleonic warfare changed things. But my favorite work on why things changed, titled, "The Art of War in the Western World" is not at my disposal at the moment. It is locked in a box 6000 miles away.

However, even if the Napoleonic style of warfare reduced the importance of such forts and siege operations, it did not nullify them and their effect would have certainly been felt in Picardy, Flanders, and Batavia had a campaign been waged for any serious amount of time to take the regions by force. After the failure of Waterloo, the chapters covering the subjugation of the allied region of Flanders by Napoleon were, unfortunately (or fortunately), never written. For the purposes of this thread, the campaign might have been fascinating.
When free of this mess of fortifications in the lowlands, even campaigns in the 1500s, 1600s, and 1700s could sport maneuver and capture of territory along Napoleonic lines. For instance, Marlborough's 1704 march up the Rhine and subjugation of Bavaria after years of bogged down warfare in Flanders, or Charles XII of Sweden's campaign's through Poland and into Russia. It is my argument that the heavy system of fortification in Picardy-Flanders-and Batavia are what bogged down these wars and that Napoleonic war would have also bogged down in them (but not to the same extent--as artillery was improving its abilities every few decades).
Fortified cities would stop or slow many Napoleonic armies--or make life extremely complicated. Take Acre in 1799 for example. This was a Napoleonic humiliation. Yet, this was just one fortress! And it wasn't even a modern one--it certainly hadn't been designed with artillery in mind from what I have seen. Yes, at Acre, Napoleon's siege artillery was lost prior to the battle, but he received replacements and he still could not reduce the defenses and take the town. Imagine trying to take an entire region like Picardy, Flanders, or Batavia. According to Osprey's "Fortresses of the Peninsular War", "In the course of the Peninsular War, Wellington’s army fought several hard battles and smaller actions, but it was the bloody sieges that troubled him more than anything else. Indeed, the performance of his army during the sieges was probably the most disappointing aspect of what was otherwise an extremely successful campaign."
After England's declaration of war on France in 1803, Napoleon joked how quickly he could conquer Britain after an invasion because of its lack of fortifications. I can't find the exact quote now, but this does show that even Napoleon had a respect for fortifications. He might have also gained part of this respect at the Siege of Toulon in which he participated in 1793.
In Osprey's "The Vauban Fortifications of France", the statement is made: "...the density and solidity of the [northeastern] double barrier was severely tested both in 1708-1712 following the battle of Oudenarde and the fall of Lille, and again in 1793-94, when the chaotic state of the revolutionary armies seemed to leave the road to Paris open once more. In neither case were the enemies of France able to make significant progress through the frontier barrier, but became bogged down in it instead." Osprey claims that 60% of Vauban's work was dedicated to the North and Northeastern perimeter of France. Interestingly, the book also claims that Paris would be only properly fortified in 1840, although Vauban had called for this as well. The Napoleonic wars introduced conflicts with "deep" invasions which overshadowed the border wars fought before and heralded a change in thinking about what was necessary.
A full list of 160 fortresses in France and their updates can be had in this Osprey title (even where the original miniature models used for planning are currently located--mostly in the L'Hotel des Invalides in Paris and in Lille). As the book also includes a full chapter on why the strategic defense in depth was important, I think I will be purchasing this very soon.
Another factor which
may have lead to a change in the style of warfare from the War of the Spanish Successon to the time of Napoleon was the fact that the armies had increased in size dramatically, allowing, perhaps, for a
Coup de Grace on the battlefield and following by controlling massive portions of the country. During the wars of the Spanish Succession, field armies comprised of ca. 50,000 men for even the largest battles. By the Napoleonic era, this had more than doubled. Indeed, the nature of warfare had changed enough to delivering defeats so large, that psychological resistance crumbled (I have seen this arguement elsewhere), whereas in earlier times it may have well been that the small armies advancing on a single city failed to inspire such fear and failed to deliver such military capacity to subdue the defeated enemy. For instance, at Ulm (a well fortified city) in 1805, after Napoleon inflicted demoralizing losses on Mack outside of the walls (5-10 km to the north and east), the garrison was surrendered. A fact which still wonders me. In some cases, you just couldn't fit 100,000 men inside a fortress for a defense which would take advantage of them all. So, your forces (most of them) were deployed outside of the walls, with all of the benefits and disadvantages which followed.
At Dresden, Napoleon fielded 135,000 troops in the defense of that walled city (the allies had roughly 230,000 present). Many of the French units were placed around the city and weren't even kept inside of it. The numbers which were so often present precluded it and encouraged maneuver around the city. Options like this weren't even available 100 years before. Certainly, the appearance of armies of Napoleonic scale changed many aspects of war, if this was one of its impacts can be debated. Yet control of these fortresses--strategically located on lines which enemy supply would have to be transported in on--would remain important, even for Napoleon and his contemporaries.
However, I tend to lean to the notion that with such large armies at their disposal, "Napoleonic Era" generals could for the first time afford to bypass such fortresses and leave behind sufficient forces to cover them and prevent the garrisons from raiding their supply lines. You need a lot of troops to completely cut off a garrison in a small city. (Which reminds me, I really hope that the troops in a garrisoned city can destroy unguarded enemy depots which are present in their provence in CoG:EE--I think they can, and it is a critical aspect in representing the importance of fortresses. I also hope that the more troops there are in the garrison, the more likely the destruction of the depot is)
However, again, I do not consider myself to be an expert on warfare. So I am always interested in hearing other people's opinions.
Below is the French system of fortifications installed by Vauban as shown in the Osprey's title, "The Vauban Fortifications of France". Again, this is just the French side of things and does not show similar work done in Flanders or Holland by its enemies. Note the close match with the "Campaigns of Marlborough" map above (you will find these cities match with all of the strong French fortresses). This leads me to believe the authors also did their homework on the non-French fortresses as well (indeed from my other reading, they have). I wonder if it would be worth getting a peak of the "Campaigns of Marlborough" map in whole, without the rules covering it?
P.S. I was just informed that in Forge of Freedom, there are 2-3 fortresses in some regions, which all must be taken to take the "provence". Is this true?
