On the immobility of wards (and Aegis)

This is thread is meant as a focused offshoot of the discussion on "container" Targets (Circle, Room, Structure, Boundary - and I guess also Aura, Road, and possibly Fire and Storm) ensuing from the most recent proposal by David Chart.

The proposal is simple and elegant. Spells targeting containers can work in two ways:
Type 1: they affect, while the spell lasts, all valid targets that were in the container at the time of casting. Type 2: while the spell lasts, they affect all valid targets that happen to be in the container, for as long as they remain in the container.

The proposal ends with a sentence on wards (which, to be fair, can be easily excised by any troupe wanting to house-rule it away without side effects). Wards, including the Aegis, are always of Type 1, and target the volume inside the container. Thus, they effectively work as Type 2, except that if the container moves, they remain anchored in space where they are. So if you ward a chest against water (with T:Room), water cannot enter the chest as long as it remains stationary. After that, it can enter the chest, but it still cannot enter the empty space previously occupied by the chest.

I dislike this last addition, because seems to add nothing to the game while being harmful in at least two ways.

The first is aesthetic, and it has two parts.
a) One thing I like of ArM5 is that you cannot target abstract space. You cannot dispel all magic in a cube of side 20 meters. You need a symbolic anchor: you can dispel magic in a circle, in a building, etc. This remains true in the entire proposal, except for lingering wards. A ship on which you cast Aegis of the Hearth, or Ward against Demons, leaves behind a ship-shaped "magic field" as soon as it moves. I find this very un-mythical.
b) In addition, this provision adds a level of complexity to the entire mechanic of containers; even though David Chart was very, very good at rephrasing everything in such a way that it was as simple as possible.

The second is about game dynamics, and it also has two parts.
a) A number of saga-enabling effects suddenly become impossible. For example, long ago we played a saga with a covenant built on the back of a gigantic sea-turtle that took it around to new locales. Under the new proposal, the covenant would not be able to have an Aegis. It also would not be able to raise the wards that kept water out when the sea-turtle dived, as it occasionally did bringing us to explore hidden underwater stuff! There are many other similar folklore effects that, although not essential to a saga, would be neat and become impossible: wards against vermin on wagons, wards against demons on a ship cabin, etc.
b) I suspect that there are shenanigans that can be played out with the "immobile afterimage" of a ward. One thing I find particularly ... ugly, is that if you want to create a ward in abstract space (say, a big tetrahedron, 10 meters to the side, hanging suspended 2 meters above the ground) you can create a D:Mom container, ward it, and then have the ward remain as the container vanishes. I suspect this could be abused.

This thread is then meant to discuss:

  1. the advantages of the "immobile wards" provision (I see none, but...).
  2. the "aesthetic" disadvantages.
  3. the "practical" disadvantages.

I'm pretty much with you on all accounts. If somebody really wants to make mobile wards impossible in their campaign, I'd be much quicker to rule that removing the focal point simply renders the spell illegal and functionally dispels it, in the same way that Ring/Circle spells end when the ring is broken, but applied more broadly. But I also think that Type 2 is, as a general rule, far more adherent to how object-based magic works in basically every folklore since forever, which is at least ostensibly the basis from which Mythic Europe draws its physics. Spatial locking can occasionally create interesting challenges, but I don't think it's worth the larger loss in story and covenant concept opportunity.

Also, this is kind of a tangential issue, but wouldn't type 1 interpretations mean being in an Aegis causes Warping to the entire covenant?

I think that would handle it better, too.

The Aegis should warp everyone inside. It only doesn't because it's a special exception in that regard, which does indicate you might be able to do original research to invent other spells that don't warp, too.

It makes sense to me in-universe why the Aegis doesn't Warp, at least insofar as "it's based on the Parma Magica and having that up doesn't Warp you," although then again the Parma Magica doesn't typically have to penetrate someone else's MR to provide MR against their effects and the Aegis does have to penetrate to penalize, so there's obviously some liberties at play no matter what.

Anyway, it was a minor tangent. I'm still of the view that mobile wards are more sensible and thematic than other interpretations, as long as you remember to follow the "resistance doesn't produce force" rule. Like the "covenant is warded against water and turtle under covenant dives down" situation basically works for me since it's the un-warded turtle displacing the water by moving and then the ward just stops it from flowing back in over the turtle's shell, but you couldn't pull a Moses by warding yourself against water and just walking into the ocean, because the ward can't physically push stuff out of the way. (Granted, if you're good at ReAq anyway, making an effect to split the sea wouldn't be THAT hard.)


Actually, I'll derail the thread a little to highlight this excellent point.

It's a very cool, characteristic aspect of how "resistance" works in ArM5, unconventional enough to create interesting situations, and at the same time very "mythic". It's also something that might need some attention in the errata, because some Wards, like Ward against Wood, do not seem to work quite in this way (whereas they should, in my opinion).

Also, there are canonical spells with Circle target being mobile.

Aegis needs to penetrate to keep a being out. But there is no need to penetrate against the being to provide you magic resistance against a spell/effect it sends through the Aegis to hit you.

Iirc, the Aegis doesn't need to penetrate if the spell comes from outside itself, but does if the caster has entered the Aegis? Serf's Parma, tho.

Basically yes, though they really are two different mechanics.
The Aegis blocks "foreign" spells originating outside unless their penetration exceeds the level of the Aegis -- in some sense it's the outside spell that needs to penetrate, and the Aegis resists.
The Aegis also penalizes "foreign" spellcasting within its boundaries, by half its own level. For this to apply, the Aegis must penetrate the magic resistance of the spellcaster.

I think that somehow a simpler definition of the Aegis effects should be possible, but still...

My understanding is the Aegis needs to penetrate to block beings with might from entering, just as wards vs supernatural being do, but the other effects of the Aegis (reducing casting total/penetration of spells or effects used within by those not invited or part of the ceremony, requiring spells from outside to penetrate the aegis, reducing the effectiveness of items) do not need to penetrate as they work upon the spells/ambient vis/other narrative reasoning, not upon the caster.

For our saga, we've ruled the opposite: creatures need to penetrate an Aegis to invade it, or a ward to penetrate or (in the case of a summoned being) try to escape it. So we've given Creatures with Might a Penetration roll (stress + Might Score). Similarly, a non-resident magus we wanted to keep "quiet" in our covenant by not giving him or her an Aegis token would have to penetrate the Aegis to cast a spell.

Irritatingly, in 4th ed. rules, the two individuals above have different target numbers to penetrate against. But it's not as inconsistent as the game I played before...

On the actual gist of this thread: I'm of the opinion if an Aegis is cast on a Boundary defined by the bounds of a mobile structure (e.g. ship), the Aegis should remain attached to said boundary, not its original location. Same if the Boundary was a tectonic plate (Paradigm, schmaradigm, game mechanics!), if you keep casting your Aegis in Los Angeles it will eventually be on an island west of San Francisco, more or less.

There have been examples of or for mobile covenants in published ArM books at least as far back as ArM3 if not before that. There's no point in ret-conning your own published cool ideas into incompatibility, IMO.

In fact, that's why I never bought a WotC product except PoD AD&D2e material.


Sure. That is a perfectly acceptable house rule but it goes against RAW.

So on the one hand, as mentioned in the other thread, I don't care what conclusion the thread and/or Mr. Chart come to, because I'm going to continue allowing mobile Aegises and other wards regardless, whether it ends up as a house rule or not. Too much cool stuff depends on it, and I'm less concerned with the edge cases it enables than the edge cases of "ghost Aegises" and similar being left behind when a mobile Boundary moves.

Other people have covered the main arguments in favor of this position ("it enables cool stuff, including cool stuff with precedent" and "it feels more mythic") fairly thoroughly, so I'm gonna take a minute and go over some of my thoughts on the possibilities for what happens when two boundaries intersect and how, notably, they're all good story fodder.

The general principle I'm working from is that 1) if it is possible for both to overlap while remaining in effect, they do so, and 2) if overlapping Boundary effects are fundamentally incompatible, you compare Penetration and the higher-Penetration effect suppresses the lower-Pen effect where they overlap.

(Oh, and just like in every other case: wards can't exert force. If a mobile aegis moves across the lair of a creature with Might, that creature is now within the Aegis, subject to the Casting Total penalty, but not expelled, exactly as if it had been invited inside and then its invitation revoked. And so on.)

The specific case someone mentioned about a covenant on a cloud floating over a covenant on a hill, and what happens when their Aegises overlap? Well, in the long and storied tradition of "a thing is inside the circle if the thing is inside the circle", no, they don't overlap; the covenant on the cloud has its Aegis that covers the covenant and its stuff on the cloud, and the covenant on the ground has its Aegis that covers the covenant and its stuff on the ground. If the magi up in the cloud want to assault the magi on the ground by dropping conjured boulders, they'll have to penetrate the groundbound Aegis just like any other spell cast toward the Aegis originating from outside it; if they want to ReTe existing boulders, that'll work just fine. In both cases this is no different from a magus standing just outside the Aegis on the ground.

But none of this addresses what happens when two Boundaries do overlap: what happens when a covenant on a big ship sails into a covenant whose Aegis covers its docks?

My inclination- and I recognize this is not strictly RAW- is that since both spells can remain in effect, they do! Both covenant's magi are subject to a casting penalty in the area of the overlap, unless they receive an invitation and casting token from the other covenant. (Both sides, but particularly the mobile side, and trebly so if the mobile side has control over its motion like a fleet of ships rather than being random like a floating island), are open to charges of "depriving of magical power" if they don't provide said invitation and token, since their spell is necessarily hindering the casting and research of the other covenant's magi.

One could make a reasonable argument for extending the "moving a ward can't exert force" principle to "moving an Aegis over an existing spell doesn't fizzle the spell, even if the spell would fizzle if it tried to enter the Aegis", but in the case of two spells both of which are Aegis of the Hearth, and only one of which is moving, it's quite possible that the mobile Aegis would compare its penetration to the stationary Aegis' level and fizzle out if it could not penetrate. As this renders mobile Aegises vulnerable to high level low pen Aegises raised in their path like land mines, I find it somewhat problematic, but- given the vis cost of high level Aegises- not overpoweringly so.

...I have been up for entirely too many hours at this point, so I think I'm just going to post this as-is and hopefully it will be of use to someone.


I think that while this looks like it might pose a serious problem the conditions for what you describe to happen are not likely to occur ever.

A mobile covenant really has to be either a ship, a submarine, some sort of flying structure or perhaps something that burrows if you want to get really creative.

for it to work on a ship or a flying struture you need to find some boundary to cast the Aegis-landmine on that the craft can still pass through. What boundary would that be? for a ship you might be tempted to say an island, but then the ship would have to beach itself for the landmine to trigger, in which case the ship is already beached, with that being the much larger problem.

For a submarine or burrowing craft you encounter a similar problem: you need to find a well defined boundary for the aegis to target but also one that the craft can pass through.

The only exception I can think of is if you cast an Aegis over an entire atoll and then a ship protected by its own aegis sails into the Atoll. But the lagoons encompassed by atolls tend to be quite large by Ars magica target standards, and also atolls dont really exist anywhere close to mythic europe.


What if you go to a tidal island (like Lindisfarne as an example) and cast an Aegis on the causeway at low tide? This could be done for the very sensible reason of preventing beings with Might from crossing over. When the tide comes in, the causeway is still present but submerged. Ships trying to go over it, or a flying aegis that is travelling up the coast, could hit it accidentally.

maybe but warding the causeway would not extend to the water above it when it is flooded. Meaning that a warded ship could safely sail over it at high tide and not sail over it all at low tide.

Similar to the earlier example of a cloud-based covenant with an aegis flying over a ground based on with another aegis dont cause any interaction between the two aegis because they are affecting different areas.

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As usual, the very first step would be to clearly ask yourself: where does the Boundary extend to?
This is a judgement call that's always required for Boundary spells, so it's not an Aegis or Ward-specific issue. In your case you have to decide whether the causeway's Boundary only affects the causeway itself, or it extends all the way up to the sea surface (I'd probably rule so) or to the sky (nah) or something else. This is necessary, for example, to rule what happens to those beings with Might regardless of any other Aegis coming around.

Once you have decided where the Boundary lies, it works as thepsyborg presented.

If a mobile Boundary enters the fixed Boundary, and neither is disrupted (e.g. because the ship crashes on the causeway, terminating any enchantments anchored to the ship's own Boundary) the usual Aegis rules apply. The mobile Boundary's enchantments are resisted by the fixed Boundary Aegis (assuming they are foreign to it, that is), and if the fail to penetrate its level they fizzle out. The reverse does not happen, because it's the mobile Boundary that entered the fixed Aegis, not the other way round.

If the mobile Aegis does not fizzle out, you now have the same situation you'd have with two "concentric" Aegis, where first one was cast over the whole causeway, and then the second was successfully cast over the boundary of the ship. They both apply simultaneously, there's nothing difficult with that.

Let me finish by saying that yes, if you wanted to cast many high level Aegis to serve as a landmine against the possibility of a flying ship (regardless of whether it's protected by an Aegis itself) landing or flying very low over them ... hey, I don't see any problem with it. You probably have rooks and rooks to waste every year, good for you :slight_smile: