Fortresses have fantastic HP and VIT, and pretty poor everything else. They can take physical beatings like it's nothing, and while their low TEC hampers their elemental defense, they have enough HP to be able to take a few elemental hits too. Unfortunately, their low DS leaves them vulnerable to having disables inflicted on them—less than ideal for a class meant to be protecting others from harm. Their low STR also means that any damage you can deal with them should be treated more as a nice bonus alongside their defensive utility. Low AGI isn't as big an issue as it is for other classes, at least, since shield skills all have very high speed modifiers. Low TP is also less of an issue than it seems, due to the fortress class skill.

An absolute necessity. A fortress's job involves being targeted by enemies a lot, so their class skill will give them a very high amount of TP back over the course of a trip into the labyrinth, or during a boss fight. At max rank, using Party Shield to take all five hits of a party-target attack will restore 25 TP, which completely refunds the cost of using Party Shield, and then some. Once you reach Master, even, you can have your fortress unleash high-cost attack skills to contribute damage with both Vengeance Bash and Earth Break, and continue to both protect the party and get TP back through Weak Shield.

A basic attack skill. Between fortresses having low STR and Bolt Strike's low damage modifier, don't expect tremendous numbers out of this skill. On the other hand, it's the cheapest attack skill in the fortress skillset, and it has elemental coverage, in case you're dealing with enemies that resist all physical damage types.

Is it worth dropping a whole 10 skill points to get the full damage, though? Not really.

Holy Smite is okay for patching up minor damage in random encounters, but isn't particularly great for FOEs or bosses. Unlike Bolt Strike, despite Holy Smite's damage not increasing much at rank 10 compared to rank 1, I do think it's worth maxing out Holy Smite if you're relying on a medic, since the amount you'd heal from a given use of it increases by 50% at rank 10 compared to rank 1. The TP cost is rough early on, but also doesn't go up much as you put skill points into it.

The first shield skill, useful for protecting a specific party member when you're confident that everyone else can handle themselves. Has a variety of uses, though in my opinion, the best ones are "protecting a party member that has Vanguard active," "protecting a party member that has Blood Surge active," and "protecting a party member that is preparing to use a Drive skill."

Useful for situations where your fortress can't tank multiple hits without risking dying, I suppose. It's also worth drawing attention to the fact that this is a party-target buff, which are pretty rare in EO4. The main issue with Strike Guard is that, eventually, fortresses will get so many personal buffs and passives that there's little need for them to buff other party members' defenses.

Element Guard's actually a fairly unique skill for EO4. This is the only elemental defense buff available to the player—while the elemental Runes also provide defense against elements, they can only protect against one element at a time. Plus, generally, you'd want to use those for offensive purposes, rather than defensive. Guard Tango, also, only affects physical damage. Since fortresses can have problems attempting to tank elemental attacks, you could use Element Guard to instead help the rest of your party soften the blow from said attacks.

A fortress's bread-and-butter skill for dealing with random encounters. Highly effective and takes barely any SP to max out. Unless you're at the very end of the game and completely retooling your skill builds exclusively for boss fights, there's little reason not to have this maxed out.

Only somewhat-negative thing to note is that due to the way aggro works, the scaling on Taunt is kind of wack. You get a lot of value from ranks 1 to 3, but rank 4 doesn't provide much of an increase to any scenario. If you really want to save on SP, you could opt to skip it.

At max rank, Auto-Taunt will save you a turn of having to set up Taunt, and instead let your fortress either start defending, or get right to smacking enemies with their mace. I like having it, personally, especially since it doesn't eat much SP.

An attack skill on a tank class that synergizes with the class's main purpose? What a novel idea.

Vengeance Bash can reach absolutely nutso damage if your fortress gets whacked enough in the four turns you have to get whacked—the cast turn, and then the three turns after. There's a certain point with damage modifiers where, no matter how low the user's attacking stats are, you'll deal a good amount of damage anyways. Invoke Gods in EO5 was like that, and Vengeance Bash has the potential to be like that. It caps out at 1500% damage, for heavens' sake. While the delay means it can be difficult to sync up with other party members' burst windows—imperials using Drives, other characters using charged-up attacks—and it also means the skills' actual damage-per-turn isn't anything spectacular, it's still damage you're getting for having your fortress do their job.

Basically, my thinking goes that while Vengeance Bash isn't necessarily the most optimal way to have your fortress spend a turn, if they've got a spare turn where they don't need to guard anyone, you might as well set up Vengeance Bash and gets some damage for having your fortress doing their job.

The first shield skill that covers multiple party members. The downside to these, compared to Ally Shield, is that they're significantly more expensive, and the damage reduction the fortress gets is heavily reduced, from 35% with a max rank Ally Shield down to 15% with a max rank Line Shield. Still, you're pretty much going to have to grab Line Shield for the midgame, as multi-target attacks start to become the norm for FOEs and bosses.

Same damage reduction as Line Shield, it just costs twice as much. Party Shield is less of a "get this" skill than Line Shield, in my opinion, because the back row already has incoming physical damage halved. It's somewhat similar to the problem with Back Guard in EO games with protectors—the back row, often, doesn't need any extra defensive assistance. By the time party-target attacks become the norm over just other forms of multi-targeting, you'll have Weak Shield, which is a far more flexible defensive option than Party Shield. I'd honestly recommend only getting Party Shield up to rank 3, so you can get the aforementioned Weak Shield.

Not the best passive to drop skill points in. There's plenty of ways to immediately recover from disables in EO4, especially if you're running a mainclass medic, so reducing the time your fortress needs in order to recover from disables doesn't provide a ton of value. If Knight's Boon could cause disables to fall off on the infliction turn, then it would be worth grabbing. Oh well.

It's Prevent Order from EO3, but it's on the defense class rather than the buff class.

Complete infliction nullification is very good, even if you do have to spend a turn not using a shield skill in order to apply it. It's good for random encounters as insurance against, say, panic or sleep inflictions, and it can sometimes render FOEs that rely on an ailment as their primary gimmick far easier to defeat.

Now, of course, what I said there mostly applies to Refresh Waltz, a skill that basically does Holy Blessing's job better than it does. While Refresh Waltz does not completely block ailment inflictions—meaning you can still lose a character's action to panic or sleep—it can still get rid of it on the infliction turn, which is the next best thing. And it lasts for multiple turns, to boot. If you're running a dancer alongside your fortress, then there's little reason to grab Holy Blessing. If not, though, then it's a decent skill to have available.

Rampart is fine enough in the midgame, before fortresses have access to the many, many passives that increase their survivability about as much as Rampart does, but after that, it's not worth the turn needed to set up. Also, the scaling is quite poor for a self-target buff.

Not a great skill, but possibly worth dropping points in once you've got Weak Shield going. Since one of the strongest applications of Weak Shield is being able to defend while also taking hits for other party members, Healing Wall at max rank would give 40 HP every time you do that, which isn't very much by the time you get Weak Shield, but it's still free healing.

I'm trying to cut down on just saying "pass" to skills without much explanation as to why, I really am, but... Pass.

A luxury skill for when your fortress is just laughing in the face of death. The damage modifier is quite high for a fortress attack skill, and the self-damage counts for increasing Vengeance Bash's damage. I say it's a "luxury skill," though, because that TP cost is exorbitant. At level 99, without any TP-boosting passives or equipment, a max rank Earth Break would cost nearly 20% of a fortress's max TP, so its ability to be spammed is limited—which goes against part of the point of the skill, increasing the damage of a queued-up Vengeance Bash. Even the TP restore from the class skill only helps so much, since tanking a party target attack would only restore 25 TP with the max rank of the class skill.

Still, it's not like fortresses are particularly starved for skill points once the lategame and postgame roll around, so there isn't much reason not to keep it in your skill list, I suppose.

The shield skill that completely invalidates the previous shield skills. All you have to do is have your other party members walk on damage tiles, or otherwise get hurt, enough to drop them below 50% HP, and Weak Shield will let your fortress take attacks for them while still being able to perform other actions.

Want to use an attack skill? Go ahead, everyone's still covered. Want to defend? Perfect, you get to halve the damage of the attacks you're about to take, for a whopping 0 TP. Have the fortress restore their own HP or TP, so that another support class can use a skill to enhance other party members' attacks? It's yours, my friend, as long as you have enough HP. And keep the Weak Shield buff up.

This skill is so amazingly good that when EO2U brought it back as Protection Vow on beasts, they had to severely nerf it by adding a cap on how many times it can activate each turn, in addition to making it chance-based; each time Protection Vow activates, the chance of it activating again on that turn is reduced. At least the damage reduction was heavily increased to compensate.

What's better than passives that reduce the damage you take from attacks? Passives that just stop attacks completely, since completely nullifying an attack means you don't have to deal with additional effects, like debuffs or disable infliction attempts. Every fortress should have Guard Mastery maxed out.

The only downside to Guard Mastery is that, if it nullifies an attack, the attack does not count for increasing Vengeance Bash's damage, but I think the benefit of negating damage and additional effects outweighs the penalty of losing Vengeance Bash damage.

There's zero reason not to grab HP Boost. It provides a ridiculous amount of extra survivability for being a passive. Hell, +40% max HP at max rank is comparable to the amount of effective HP that a max rank Rampart would provide, except HP Boost is, again, a passive.