See title. For those who are unaware, shieldwall is an ability under Path of the Defender, which gives +5 defense to each group in the army (including the one who has the ability.
This is a pretty big thing. as anyone who's played the game much will realise, defense is an incredibly important aspect of this game. I'm not sure about the math behind it (i'd love to see formulas) but my intuition from the numbers i've seen tells me it probably works, to some degree, on flat reduction. If so that would make every point of it incredibly powerful.
The crazy thing about shieldwall is that it grants that defense to anyone, including people who have no armour, no shields, no magic trinkets, etc. nothing. Or perhaps it's crazier still that it apples to people who already have all that stuff, pushing their defense to new heights. It's certainly a good reason to pick the path of the defender, if nothing else.
But it has farther problems. The first and most important of which, is that it's stackable. If multiple people in an army have the shieldwall ability, then everyone in the army recieves bonuse defense of 5x the number of instances of the ability. Theoretically up to 9 of them. Personally i think this is pretty absurd, in fact it's a general problem that throughout this game many things are stackable which really ought not to be, and our beloved developers need to take a slightly closer look at limiting a few things. 
The worst problem of all, the problem that ironically stacks with the previous problem and compounds things, concerns the Altarian Kingdom. They have the ability to train "Henchmen", mini champions who can wear equipment and select skills on levelling up like normal champions, but are designed like normal units, including the ability to pick three starting traits, like any normally trained unit. Henchmen units have access to the same pool of offensive and defensive abilities as normal units, but they also have three special abilities. Bard, which gives +10% xp to the army, Cook which gives +1 healing per season, and Shieldwall, which is previously described. If that's not clear, the altarians have the ability to train a unit which has shieldwall by default, and thus can reach an army of 9 shieldwall units with relative ease. So it takes 450 influence, big deal. Who actually uses influence for anything else anyway? I find myself with tons of the stuff in every game, and nothing to spend it on.
I think being able to have an army with 45 free defense each, on top of whatever armor and accessories they might be wearing, is a bit much. even the +15 that i have in my current game feels a bit much, i'm laughing off physical attacks from dragons already and i'm not even 100 turns in. Shieldwall needs some nerfing.
The clearest and simplest way to fix it that i can see, is to make it non stackable. make it a unique, exclusive bonus. One unit with shieldwall in the party gives +5 defense. two units give +5 defense. nine units give +5 defense even. Make only the first one count, and the rest do nothing. it would also be helpful to mention this in it's tooltip 
