[4E] Magic Circle: Viable city defense?

[Enlong]

So, I was looking at the Magic Circle ritual, and I realized that, while a sufficiently large magic circle takes a huge amount of time to inscribe, the ritual cast upon a circle of any size still only takes one hour to cast, and the component cost is always 100 gp, no matter the size of the circle. So I was wondering if it would be a viable strategy for a militarily-minded city, or castle, or whatever, to use Magic Circle as a sort of first line of defense for large armies. One "All" circle, or six lesser circles, one for each type.
They could make and maintain the circles in peacetime so that they could quickly activate the thing whenever an army looms.

What do you think? A viable strategy?

[Aron Times]

It would be effective, but breaking it only takes a standard action. Granted, you have to find a creature whose level equals the ritual caster's Arcana check result - 10, but it can leave a city wide open if it is broken.

Also, the "All" option literally blocks all creatures, so nothing can get in or out of a sufficiently powerful Magic Circle vs. All.

The best defense is a good offense. Basically, if they're too busy defending against your attacks, they're too busy to attack you.

If that is not an option, might I suggest defensive structures lining the perimeter? Blaster traps are basically pop-up machineguns crunch-wise, so you can use them to defend your Ultimate Fortress of Doom.

[Johel]

If we are going the trap road, Summoning traps are a must.
A single Summon Monster III trap (CL5) can basically summon one Huge Fiendish Centipedes per turn. By turn 5, there are 5 of these monsters guarding the area. This number never decrease afterward, as one centipedes disappear and another appears each turn. No need to even aim, just activate and let it swarm the invader.

Also, if you want the ultimate defense, use Forbiddance.
It's costly but it's safer. Of course, you have to let a single opening for your people to get out without being killed if they have the "wrong" alignments.
It's permanent and can only be dispelled if the enemy has a higher CL than you.

[Enlong]

If we are going the trap road, Summoning traps are a must.
A single Summon Monster III trap (CL5) can basically summon one Huge Fiendish Centipedes per turn. By turn 5, there are 5 of these monsters guarding the area. This number never decrease afterward, as one centipedes disappear and another appears each turn. No need to even aim, just activate and let it swarm the invader.

Also, if you want the ultimate defense, use Forbiddance.
It's costly but it's safer. Of course, you have to let a single opening for your people to get out without being killed if they have the "wrong" alignments.
It's permanent and can only be dispelled if the enemy has a higher CL than you.

Ah, I should've been more specific. I'm talking about 4th Edition, and the applications of the Magic Circle Ritual from its PHB1.




Now, to Joseph. Great suggestions, thanks for those. I never intended Magic Circle to be the only defense anyway, just a first line of defense before they reach the standard blasters and such. Something to slow them down.

[Akal Saris]

I think it's been done, sorta-kinda. In 2E, one of the cities in Thay was constructed to be a massive Protection from Evil 1 thousand ft radius/Binding spell, keeping a powerful demon bound within it and preventing other demons from entering - but each map made of the city reduced the power of the seal by a tiny fraction.

I think at the end of 3.5 or the start of 4E the demon breaks out though, which disappointed me. I didn't read much about that though, since I was sick of all the ridiculous things that simultaneously happened in the 5-10 year span of FR that 2E to 3.5 covers. It's one reason that I didn't mind 4E fast-forwarding the timeline - just like Dragonlance, the period had just been over-saturated.

[Asbestos]

Two All circles, one inside the other. Area is filled with blaster traps. Activate everything once some portion of the invading army has entered the magical meat grinder.

[Enlong]

Two All circles, one inside the other. Area is filled with blaster traps. Activate everything once some portion of the invading army has entered the magical meat grinder.

Ooooh. Nice one. But since the casting time is 1 hour, the city will need some scouts estimating the speed and arrival time of the army, so that the mages can start casting the ritual at the right time.

[Asbestos]

The inner ring could just be standard defenses of choice, the activation of the outer ring is the only thing that needs to be well timed. This does require Tucker-esque sneakiness though, but most seiges take more than one hour.

[Oracle_Hunter]

The real problem is that it'd be really easy to destroy:

Other creatures of an affected origin take force damage equal to your Arcana check result when passing through the boundary, but doing so breaks the circle. Unaffected creatures can take a standard action to obscure the inscription and break the circle.

So after spending days of inscribing Circles against Aberrant, Elemental, Fey, Immortal, and Shadow, some kid scuffs a rune as a standard action and the whole thing is destroyed.

Plus, you get the 1 roll at the end of the Ritual. Still, it is something I've thought about:

A DC 21 check stops all Heroic-level monsters of a particular type (DC 26 for an All)

A DC 31 check stops all Paragon-level monsters of a particular type (DC 36 for an All)

A DC 41 check stops all Epic-level monsters of a particular type (DC 46 for an All)

Since you can get 4 Assistants (+8 Arcana) this means an Eladrin (+2) Wizard (INT 18, +9 w/ Training) can perform the Heroic Blocker at LV 2 (+1) on a roll of a 1. With Skill Focus (+3) he can do a Heroic-All Blocker at LV 4.

Amusingly, Teleportation may not be affected by Magic Circles:

Instantaneous: When you teleport, you disappear from the space you occupy and immediately appear in a new space you choose. Creatures, objects, and terrain between you and your destination don’t hinder your movement in any way.

Of course, I'd be inclined to construe "pass through" liberally, but by RAW...

[Enlong]

Well as for the whole "A kid scuffs it", you're forgetting that, even if we don't use "All" circles, "Natural" is one of the choices. So if we're using two rings, the innermost one would be Natural so that ignorant townies can't screw it up.

Though, even if we use a bunch, the army could just send in single recruits who aren't affected in order to mess it up, so I'm thinking All rings are the best choice after all.


And the teleport thing is funny, too.


Also, how long would it take to repair a broken Circle? By RAW it doesn't say, but how would you rule it? It'd depend on how much of it got scuffed up, I'd say, and then of course the ritual would have to be re-cast... I imagine a city using it as an anti-siege weapon would keep the runes covered so that kids can't scuff it, and then uncovered when it's needed.

So the general vibe I'm getting is that it's an interesting idea, but the amount of time it'd take to create a barrier that can be broken as a standard action by an unaffected subject means that it doesn't stand up on its own, and is only good when used in conjunction with other, standard deterrents, like Traps and, you know, an army. Does that sound about right?
I still like it for the flavor though; I like the idea of a city pulling out one or several Magic Circles to put the place into "lockdown"

[taltamir]

permanent rings are doable... make them out of a tough material like steel... good luck breaking it.
If you need one on the spot, you should DRAW on with chalk... but if you have a location, you can make a permanent one from a tough material that is essentially unbreakable

[Oracle_Hunter]

permanent rings are doable... make them out of a tough material like steel... good luck breaking it.
If you need one on the spot, you should DRAW on with chalk... but if you have a location, you can make a permanent one from a tough material that is essentially unbreakable

Well, not by RAW you can't

@Enlong - I didn't include Natural because I presumed you wanted to be able to leave your own city. Remember: you don't get a pass from the Circle, even though you made it.

Of course, if you allow Teleportation, then the Circle becomes silly (Step 1: Be an Eladrin ).

EDIT: There is no such thing as a "broken" Circle - it's either there or it ain't. Once the enchantment is ruined, you'd have to remake the whole dang thing.

Now, if we're talking about static city defenses - well, I introduced a "Death Ward" in my game as a protection around an Epic Wizard's tower. It's pretty simple - try to pass it, and you suffer a Fortitude attack. If it hits, lose 1d4+1 Surges.

If it misses, lose 1

To bypass it, you need a special charm (the "Key") which shuts the Ward off for 30 seconds when a being wearing the Key comes in contact with the Ward.

Anyhoo, if you wanted to 'brew up a "Greater Magic Circle" Ritual, I'd make it at least Mid-Paragon (LV 14 sounds right) and allow it to be made "permanent" in a manner similar to the Forbiddance Ritual. If the Circle is breached, anyone who can cast Greater Magic Circle can revive it by paying the Ritual Cost and performing a shortened version of the Ritual (say, 1/2 the time of the original).

[Enlong]

permanent rings are doable... make them out of a tough material like steel... good luck breaking it.
If you need one on the spot, you should DRAW on with chalk... but if you have a location, you can make a permanent one from a tough material that is essentially unbreakable

The ritual doesn't say anything about making the rings unbreakable. In fact, the passage about unaffected creatures breaking the circle only says that they can "obscure" it to break the spell.
I'm guessing that the circle breaks if any of the runes are covered up or marred, because it breaks when affected creatures pass through it as well..

But I guess you could make the runes with something more permanent than chalk so that you could recast the ritual as needed without having to redraw everything once it breaks.

Well, not by RAW you can't

@Enlong - I didn't include Natural because I presumed you wanted to be able to leave your own city. Remember: you don't get a pass from the Circle, even though you made it.

Of course, if you allow Teleportation, then the Circle becomes silly (Step 1: Be an Eladrin ).

Well, that's also true, but sometimes enemies use natural creatures to attack cities with, so you gotta think about that, too. Maybe if you want to just really lock the city down, then Natural or All become useful. Makes for a good way to wait out a siege, I guess. If you have a sufficiently powerful All circle, then nothing's getting in or out.

Unless, of course, they have Eladrin. Sneaky, sneaky elveses.

[Oracle_Hunter]

Well, that's also true, but sometimes enemies use natural creatures to attack cities with, so you gotta think about that, too. Maybe if you want to just really lock the city down, then Natural or All become useful. Makes for a good way to wait out a siege, I guess. If you have a sufficiently powerful All circle, then nothing's getting in or out.

Unless, of course, they have Eladrin. Sneaky, sneaky elveses.

Yes, but once the siege is over, how can you get out? Unless you, personally, are more powerful than the All Circle, nobody around can go out and smudge it.

And there's no control on the power of the circle - if you roll a 20, you might accidentally make a Circle that not even the Gods can cross

[Mando Knight]

And there's no control on the power of the circle - if you roll a 20, you might accidentally make a Circle that not even the Gods can cross

Gods can teleport.

[Enlong]

Yes, but once the siege is over, how can you get out? Unless you, personally, are more powerful than the All Circle, nobody around can go out and smudge it.

And there's no control on the power of the circle - if you roll a 20, you might accidentally make a Circle that not even the Gods can cross

Ooooh. Good point. Must be careful about that.

The Greater Magic Circle is a nice idea, too. Because your time is worth saving!
[/slogan]

[Kurald Galain]

And there's no control on the power of the circle - if you roll a 20, you might accidentally make a Circle that not even the Gods can cross

That would be an interesting plot. Some $&^*($^ wizard created a big circle that nobody can cross, and the princess is in another castle trapped inside...