How Aegis of the Hearth works

Spun off from the thread "What does it take to participate in the Aegis..."

If a Spell is cast into an Aegis, it is "resisted by the Aegis". Later this is defined as "needs to penetrate a Resistance equal to the level of the Aegis".
It has since the Core Book was written been Errata'ed that Aegis of the Hearth is no exception to wawrds needing to Penetrate. However I can't seem to find a Core Book Errata for this, but it is mentioned in Through the Aegis p137, insert box 'Ferra of Bonisagus', right column. It seems someone had the foresight to mention it in a book.
Maybe it is really the Penetration of the Aegis, and not simply the level which the intruding spell needs? I think not, as it seems the Penetration of for warding effects. However there are examples of comparing Penetration to Penetration, like when casting Muti VIm spells on a non-coperating magus' spells!

Next thing is spells cast inside the Aegis. Here, the Aegis enforces a penalty to casting equal to ½ level. Effectively this reduces Penetration. It is noted that Penetration for creature Powers suffers similar penalties.

What about devices? ArM5 p161, middle column, top says "Effects from enchanted devices are resisted by the Aegis".
But what does that mean? If Penetration is just reduced på ½ level, then it's simple. Devices may then have negative Penetration, but that only matters on targets with MR of 0 or more. One notes that having MR 0 is significantly better than having none at all!

But the same wording is used here - "resisted" as for describing spells cast from outside the Aegis. And here the Penetration needs to be at least equal to the Aegis level. And one could easily argue that this applies for devices as well. It actually never occurred to before it was mentioned in the thread "What does it take to participate in the Aegis..."

Last thing I'll mention is how Aegis protects from creatures with Might. They cannot enter unless they have higher Might than the Aegis level. And since this is a warding-like effect it must also Penetrate. Personally, I like this. I find it odd that a powerful ritual has so easy a time keeping creature out. If you can juuuust pull off casting a huge Aegis, it keeps the big beasts out, even though your Penetration sucks. But you can't actually cast active spells on these creatures, because other effects can't penetrate (well, maybe they can, using different Arts, but still).
By requiring penetration I think you avoid ridiculously high level Aegises (what is the plural of that?), and you have magi participating in Wizard's Communion in order to get a good Pen. I like that. We do that in our current Rhine saga. Come to think of it, I think we've forgotten to track it. It maybe time for a story with an intrusive creature...

Since an AoH reduces the casting total of a spell foreign to it, you could make an argument that it negates enchanted items that produce a spell effect less than the AoH level.

plural = aegides


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Not really, because the spells merely have reduced casting total which means reduced Penetration.
They aren’t negated, and I don’t want them to.

Spells and devices don’t function the same way. Spells are reduced in casting and therefore Penetration by penalties for wounds, aura, and other factors. Devices always work, with fixed effects, because that is the trade off with the vis cost, uses per day etc.

I’m just not sure what the intent was for device use.

  1. Is it to have them fizzle if they don’t have enough Penetration? Like spells cast outside and in.
  2. Or to reduce Penetration? Like for spells cast inside.

If 1) then devices for use inside a foreign Aegis needs Penetration to work at all.
If 2) they work fine, against mundanes but have reduced Pen and may not work on MR.

Also, for outside spells, if the Pen is at least as high as Aegis level then what? Is it enough for Pen to exceed the MR of people inside, or dies it need to exceed Aegis lvl plus MR? That’s harsh!

AotH (casting from OUTSIDE the Aegis)

If the foreign spell cannot penetrate a resistance equal to the level of the Aegis, it fizzles out.

p.82 ArM5

The penetration total may be zero or negative. For example, if a magus with a penetration bonus of 0, because he has no score in Penetration, casts a Formulaic spell with a Casting Total 5 less than the spell’s level, his penetration total is –5. If the penetration is zero or negative, the spell cannot affect any target with magic resistance, even if the score of the magic resistance is 0. However, it can still affect targets with no magic resistance. If the penetration total exceeds a target’s magic resistance, the spell affects that target. If a spell is targeted at several individuals who have different levels of magic resistance, it is possible for the spell to affect some but not others.

Given that, I would say that items need to have POSITIVE penetration (or at least zero, but I would prefer to err on the side of caution and say at least 1) to cast their effect inside a hostile Aegis. Otherwise, it fizzles out.
Given that by the RAW items have ridiculous penetration totals, I do not think this is a problem at all for the enchanted items.

Devices still work, the same as creature powers still work, they just have lowered Penetration.

I think this specific phrasing means that magic items need to penetrate magic resistance equal to the level of the Aegis regardless of whether they are outside the Aegis or not. The exception being if they are included in the Aegis by e.g. being crafted by someone who is included.

For spells, there are 2-3 different rules.

  1. Spells cast from the outside, towards the covenant under protection.
    1bis. Spell effects cast outside, when the target moves inside the aegis.
  2. Spells cast inside the aegis.

Interestingly the rules are different for the two cases (1bis seems to be a subcase of 1).

  1. The aegis provides MR equal to its level. Presumably the caster must penetrate the higher of the aegis level and the target's MR.
  2. Half the aegis level is subtracted from the casting roll. This may cause the spell to fail, or at best reduce the penetration.
    This seems fair enough. It is easier to make the effect work if you have physically entered the protected area. It is a distinction easily missed, though, especially when trying to generalise to items and powers.

By RAW core an effect with negative penetration still works, but any MR, even 0, will resist it. Casting a spell from inside the aegis on a grog or a building should work, if the spell casting roll succeeds at all. Thus casting a spell inside the aegis is not a big deal unless the target has MR.

If we try to transfer this to devices, we should keep the same distinction.

  1. An item outside, trying to affect the inside, or an effect applied outside on a target who moves inside, should have to penetrate just like the spell. Presumably the same rule applies for creatures using powers from the outside. Nothing is written, I think, about creatures' powers.
  2. An item first brought inside, has a penalty to its penetration, just like the magus. No penalty is mentioned for affecting a target without MR, nor is there any obstacle in getting the item inside.

I believe this reading is consistent and true to the letter of the RAW. Whether it is reasonable is another matter.

Now, have a look at my rustic (an ex misc line) magus fletcher/archer. He has specialised on crafting arrows as charged items, which craft magic allows him to do in hours. The arrows are shot at the target and the effect triggers on impact. In other words, he shoots the items into the aegis by mundane means, and it triggers on impact casting the effect from the insde. Without entering the aegis and without spending a season of preparation, he can thus get the softer penalty. One of the effects in his repertoir is End of the Mighty Castle at touch range, and the castle does not have MR, so penetration is irrelevant.

I am not sure my magus was meant to have such an easy time against the Aegis, and I certainly did not design him in order to break covenants.

You might refer to this that I wrote a while ago. The formatting got messed up as the forum switched over, but the content is still there.

Unfortunately, callen, you did not conclude in the case that triggered this thread, namely how to resolve items ...

Intuitively I prefer to resolve the word «resisted» by analogy to spells, as I outlined, i.e. your second option. However, I am not sure I like the consequences of that interpretation.

There is a reason I didn't conclude anything: there is no logical coclusion. That's what I presented. I did mention some options by analogy.

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I know it is a legacy spell and all, that if is somewhat outside Hermetic theory, and that the whole issue about whether or not it must Penetrate muddles things up.

I'm just thrown off by the odd phrasing about "resisting", and the not clearly defined bits about affecting devices.

I'll admit it has never, ever been an issue in any of my sagas. Now I want to focus on how I'd like Aegis to work, in a concistent and balanced manner. As close to the rules, as they are, as possible.

*Level of Aegis is the effect, the efficiency it has. So this number is used to define casting penalties (½ level) or the number a creature's Might must exceed in order to enter.

*Penetration of the Aegis is the strength when compared to other magic or powers. Since Aegis is not an indirect effect I feel a need for it to Penetrate. Also, I feel that not enforcing Penetration leads to poorly cast high level Aegis, and that ruins the feeling for me. This is what Wizard's Communion (-like spells) are for.

*When casting spells/activating devices outside the Aegis at targets inside, or cast spells/activate devices outside the Aegis and the target enters, then the Penetration of the effect must exceed the Penetration of the Aegis or it will fizzle. [design note: MuVi spells cast on another magus' spells, when not cooperating, uses the Pen vs. Pen mechanic]

*When casting spells inside the Aegis, casting total has a penalty equal to ½ Aegis level, so the spell may actually fail. When activating a device inside the Aegis, it has a penalty to Penetration equal to ½ Aegis level. When a creature uses a power inside the Aegis, it has a penalty to Penetration equal to ½ Aegis level. Devices and creature powers will therefore never fail, but may have negative Penetration. This is blocked by a MR of 0, but is irelevant if there is no MR at all.

*Creatures attempting to enter an Aegis must have a higher Might than the Aegis level, but the Aegis needs to Penetrate the creature's MR for this to take effect.

*When casting a Vim spell on the Aegis, then it's Penetration needs to exceed that of the Aegis. Furthermore the effects of the spell is gauged against the level of the Aegis as normal , to see if it can be affected.

Am I missing any situations?

Once I thought about and described the situaitons above, it seems the Penetration of the Aegis covers things breaching the shell, while the level of the Aegis affects situations inside.

I have the impression you're trying to confirm the canon behavior at the moment.

When casting spells, you look at the level of the Aegis, not its penetration. Its penetration is only for holding creatures out of it.

I was at first, then as I faced inconsistency I attempted to formulate something coherent to me.

When casting spells, you look at the level of the Aegis, not its penetration. Its penetration is only for holding creatures out of it.

Yes, but for my coherent theory, if Penetration is needed here, then it makes more sense for me to use the Penetration rather than the Level for casting spells through it.

Neither am I.

I think the intent was for them to fizzle, so that enchanted items could not easily be dropped off inside the Aegis to wreak havoc. That is, you needed a living caster inside to do damage — and that has more story potential. However, I also think that either approach could work.

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The way the spell is phrased, devices are mentioned to be "resisted" in the same way spells cast from outside are described.
So that sounds like fizzle, if device Penetration is insufficient.

Looking at how devices work otherwise, what the differences are compared to spells: A device always works, regardless of Wound- or aura penalties. However Aura always modifies Penetration (as well as MR). So a device used inside a cathedral, has 3x aura as penalties, and the Archbishop with has a modest MR from his Commanding Aura, with Aura as a bonus. So the device may prove useless, unless designed with sufficient Penetration. But against anyone without MR, it works just fine.

Do we want devices inside a foreign Aegis to work this way, or do we want the Aegis to actually be good at defending against this?
And does it nerf devices?

The more I think about it, it makes sense that devices need to Penetrate versus the Aegis to work. That way an evil magus can't just churn out simple devices of mass destruction to mundane goons. They need to be powerful! So the magus may be better of going in himself and casting spells.
And IMHO this does not make devices less valuable, they still have merits.

But using a device inside a foreign Aegis, with a Penetration sufficient to actually work, then I assume the MR of any targets is treated seperately, meaning the MR and Aegis levels aren't added.

Also, is the Penetration of the Aegis only relevant for preventnig creatures from entering?
I'd much prefer it if it was the Penetration, and not the level, of the Aegis which the Penetration of the spells from outside/devices needs to exceed. As I mentioned, this is what Muto Vim does, for affecting the spells of another magus who is not cooperating.

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In my last saga, we house-ruled that anything with a penetration below -10 fizzles. After all, if you try to cast a formulaic spell of level 20, if you get a casting total below 10 the spell doesn't go off, 10 to 19 it will go off with a negative penetration and cost fatigue, and with 20+ it goes off as intended. Using the treatment of formulaic spells as an analogue for how other effects work, this gives rise to the following:

The great many "utility items" with no penetration built in (like magic candle lighters, or chamber pots that destroy liquids inside) will function in a level 20 Aegis (minimum level for ritual) or a level 3 urban Divine aura but with a very negative penetration. If you go inside a stronger Aegis or a church with a stronger aura, they won't work. This means having a stronger Aegis gives more protection against items, but means if you buy in enchanted devices made outside the Aegis you will need to commission ones with stronger penetration.

If you allow items to function regardless of negative penetration, this is great for Verditius characters who take spellcasting flaws and want to use enchanted objects for everything, but conversely makes all covenants horribly vulnerable to enchanted items.


That is my big concern. What makes the order the toughest magic tradition is defence. The parma and the Aegis.

A devoted committed enemy can churn out a ton of middling items to kill every grog, burn every field, destroy all the infrastructure the order depends on. That seems off. I'm not saying it should be impossible, I'm saying, the resource cost should be a lot higher.

A covenant paying 8 vis a year, using wizards communion to have a level 40 penetration, level 40 aegis that doesn't meaningfully protect the covenant folk seems off.

It sounds like more and more arguments for interpreting that devices fizzle unless they have sufficient Penetration.

I think that's a houserule, but one I'd be comfortable with.