D&D 5E Standard security features of a permanent Teleportation Circle

[Lehrbuch]

Putting a circle outside the walls and then not securing it is still a massive security risk. Each casting of teleport circle can dump about 2000 well organised troops through. You really don't want to be defending a kingdom where the enemy can move troops like that, especially since they can follow that with a casting of private sanctum to stop you responding.

For a single casting of teleportation circle the portal is only open for 1 round. It seems a bit unlikely to get 2000 troops through. However, sure you can move a lot of soldiers around quickly, even if it takes several sequential castings.

But, even if the permanent circle didn't exist, you have to remember that this is a D&D fantasy setting. Teleportation is not the only way to get fast moving troops. And when dragons, undead, demons, etc are possibilities fast moving troops are just one of numerous hazards that can arrive at the city walls. Either the city wall can defend against this sort of stuff or it can't. The presence of a permanent teleportation circle near the city doesn't really change too much. And you would be foolish to have it really close --- a couple of hours march distant would be sensible.

 

[Saeviomagy]

You and I have vastly different opinions on how many people can get through a 10' portal in 6 seconds.

For a single casting of teleportation circle the portal is only open for 1 round. It seems a bit unlikely to get 2000 troops through. However, sure you can move a lot of soldiers around quickly, even if it takes several sequential castings.

The 2000 number comes from using D&D and positing "how many creatures could be standing within a dash of the circle". Remember - they don't need to clear the circle on the other side: if there is no room for them, then they appear in an unoccupied space. So ~2000 is how many you can squeeze into every square. Well, actually looking at the rules, troops can't be more than 1 per 5 foot square, so bring it down to 500.

If you want to go for realism, then the sensible way is probably to have 4 streams of troops from cardinal directions. If we assume they still can't move faster than 60' in a round, you end up with 384 in a round (but I'm putting 4 guys per 5' square because it seems a more reasonable number for trained troops doing a practised maneuver).

But, even if the permanent circle didn't exist, you have to remember that this is a D&D fantasy setting. Teleportation is not the only way to get fast moving troops. And when dragons, undead, demons, etc are possibilities fast moving troops are just one of numerous hazards that can arrive at the city walls. Either the city wall can defend against this sort of stuff or it can't. The presence of a permanent teleportation circle near the city doesn't really change too much. And you would be foolish to have it really close --- a couple of hours march distant would be sensible.

Dragons, undead and demons are not a threat on the same scale as a massive mundane foot force. If you have problems with dragons, undead and demons, you recruit the local group of 5 adventurers to go whack them. If you do that with a 2000 man army that's utilizing magic in a sensible way, your adventurers are not likely to triumph. Also dragons, demons and undead tend to require a lot more countermeasures than "just hope that no one tries it".

And you would be foolish to have it really close --- a couple of hours march distant would be sensible.

... but again, if your tactic is "put it outside the city walls and hope no one uses it", then you're still going to get jumped by a large armed force when you cannot respond. Much better to booby trap the thing or flat out disable it for unauthorized transport.

Scry, as Erik points out, isn't actually that big of a risk in this situation - especially considering the majority of the people that might like to scry on the party don't know them well enough nor have much of a connection to avoid the party member they choose to scry upon having a bonus on the saving throw to avoid it.

"That guy that I stabbed who just escaped through a teleport circle, who's blood I have on my dagger" would seem to do it. And the next scry is targeted at a location that you saw through the first one.

Plus, scrying is thwarted by Mordenkainen's private sanctum which can also be made permanent.

Sure! And that's great! But the original posit was to rely on obscurity as security. This is being more active and sensible about it.

 

[Lehrbuch]

... but again, if your tactic is "put it outside the city walls and hope no one uses it", then you're still going to get jumped by a large armed force when you cannot respond. Much better to booby trap the thing or flat out disable it for unauthorized transport.

No, the tactic is to put it an hour or so outside the city, and hope that everyone uses it continuously (and charge them a tax). Otherwise, why did we build it?

And if an army does show up, then either your city can cope with an enemy army suddenly appearing or it can't. The fact that the enemy used your permanent teleportation circle to arrive doesn't make the army any more difficult to deal with than if they used other methods to suddenly appear.

 

[AaronOfBarbaria]

"That guy that I stabbed who just escaped through a teleport circle, who's blood I have on my dagger" would seem to do it.

I think there are a lot of details leading up to not only having an enemy that is capable of scrying but has also gotten close enough to stab you - without that being the final confrontation between the two of you - and has chosen the correct time to scry on you that you aren't giving appropriate consideration to.

But yes, like any plan, the plan of securing a teleportation circle through secrecy isn't infallible.

 

[Ahglock]

How are people envisioning this spell? A circle that anyone who enters they get transported from? I ask because I see it as a circle within which is a 10 foot wide vertical portal you can walk into to be transported. Why, well because the spell says it creates a 10' wide portal. Now yes the circle is 10' wide but it would just say anyone who enters the circle if it was the entire circle and not mention creating a 10' wide portal that people enter to be transported. So my how many troops is more in the 24-48 range because I don't see 4 people per 5' square. Or if I did it would be difficult terrain but if you did allow 4 per 5' sq it would be 96 troops. I wouldn't be against 96 or a flat circle and 384 or whatever as 60 feet a movement is kind of slow. but all that mean is a small adjustment to defenses at the location. It would be a tactically bad spot like surrounded by walls and ringed with archers if you lean towards 384 a dude with a necklace of fireballs would massacre them. I mean we are assuming the magic for a permanent teleportation circle a guard with access to 3rd level spells naturally or through a device isn't a stretch. But 30 archers will go to town on people in a pit pretty quickly.

Though how this is much worse than them unloading a boat full of troops I'm not clear on.

 

[Jediking]

Teleportation Security Administration agents would be checking identities and gear of anyone who has a valid ticket to travel via a teleportation circle. The long lines, occassional strip-searches, and surly attitudes of the agents would foil many a nefarious plot.

But then they managed to alienate the important Dwarf traders because of their "random" searches didn't seem so random after Rusty Oakmead's unstable keg caught fire one time...

 

[Saeviomagy]

How are people envisioning this spell? A circle that anyone who enters they get transported from? I ask because I see it as a circle within which is a 10 foot wide vertical portal you can walk into to be transported. Why, well because the spell says it creates a 10' wide portal. Now yes the circle is 10' wide but it would just say anyone who enters the circle if it was the entire circle and not mention creating a 10' wide portal that people enter to be transported.

Well, no. There are plenty of spells that say random flavour text that doesn't affect the rules at all.

So yes, I see it as a 10' circle that transports you, primarily because there's nothing to describe it as anything else. Contrast it with the wording (and rules) of arcane gate, for instance.

So my how many troops is more in the 24-48 range because I don't see 4 people per 5' square.

Have you ever been in an exercise class, and the person running it tells you to all stand so you have space, and then he says "put your arms out and swing them around and make sure you don't hit anyone", and everyone has to move apart some more? At the end of that process, you're ~1 person to a 5' space.

It's a huge amount of room. I did a quick image search, and I couldn't see any pictures of military charges which had 1 person per 5' space. And that included cavalry charges. Now take a look at an image search of track races - again: it's only once you get to the top tiers that you're approaching 1 person to a 5' space, and that's for the benefit of spectators, not for the runners.

Or if I did it would be difficult terrain but if you did allow 4 per 5' sq it would be 96 troops. I wouldn't be against 96 or a flat circle and 384 or whatever as 60 feet a movement is kind of slow. but all that mean is a small adjustment to defenses at the location. It would be a tactically bad spot like surrounded by walls and ringed with archers if you lean towards 384 a dude with a necklace of fireballs would massacre them. I mean we are assuming the magic for a permanent teleportation circle a guard with access to 3rd level spells naturally or through a device isn't a stretch. But 30 archers will go to town on people in a pit pretty quickly.

The main problem with mundane defenses like that is that whole "appears in an unoccupied space" bit. You have 30 archers in a ring, and I send through enough people that some of them are outside your ring. The same goes for the necklace of fireballs.

You are right though - at some point you had access to a caster capable of casting 365 5th level spells. It seems like you're skimping if you don't get him to throw in a glyph of warding with something to shut it down when you need to.

Though how this is much worse than them unloading a boat full of troops I'm not clear on.

A boatload of troops is almost impossible to unload without a lot of notice. They had to embark somewhere, their movement is likely slower than a dedicated messenger with an eye to haste, and they'll be spotted enroute almost certainly. You have time to arm, bring in reinforcements, close the gates, bring your farmers and stock within the city and in general prepare for a siege.

 

[Ahglock]

Let's say I accepted all your assertions on how many people you can get through a circle in 6 seconds. Wouldn't that just make them more likely to be epic slaughtered in seconds. If while hustling you can fit 4 people to a 5'square how many can fit when jam packed into nearest unoccupied space? You could probably wipe out all 384 with a single fireball. They wouldn't be appearing outside the ring they'd be crammed in to their own doom. and if we are going with realistic when at a hustle your distance between friends gap suddenly narrows to virtually nothing are they bumping into each orher, tripping and falling. It would be the keystone cop invasion.

Similarly though if the world is populated with coordinated guys getting themselves through a circle in 6 seconds dropping a dozen gang planks and unloading the same number of men from a boat should take the same time. Either you can train people for maneuvers where they move in perfect unison in tight formation or you can't. Private sanctum on a boat so it's only visual tells that reveal. Unload a mile or 2 out of town in apparently 6 seconds per 300+ troops and march into town before they can respond.

Sorry for not quoting it's a pita on my phone.

 

[Khisanth the Ancient]

Dragons, undead and demons are not a threat on the same scale as a massive mundane foot force.

Well... that depends.

A mundane force of footsoldiers can be opposed by another mundane force of footsoldiers, and if you're defending a city, the defender generally has a significant advantage.

But some demons and undead are really hard to stop with just mundane forces.

On the low-CR end, barlgura and quasits can become invisible, shadow demons can pass through walls and are stealthy, wraiths can go through walls and animate their victims as spectres

And high-CR demons can teleport, and mummy lords and liches are totally immune to mundane weapons!

If you have problems with dragons, undead and demons, you recruit the local group of 5 adventurers to go whack them. If you do that with a 2000 man army that's utilizing magic in a sensible way, your adventurers are not likely to triumph.

Sure, but it's probably a lot easier to find enough troops to defend your city against a 2000-man army than to find a party of adventurers high enough level to deal with a nalfeshnee, marilith, balor, mummy lord, or lich. 13th+ level people just aren't that common.

 

[Khisanth the Ancient]

Either the city wall can defend against this sort of stuff or it can't.

In a high-magic world, I don't think you'd have city walls, just as modern cities don't.

If there are enough wizards capable of casting teleportation circle to make permanent teleportation circles important to trade (which implies a very-high-magic world with lots of high-level spellcasters), then war is going to be dominated by high-level characters and powerful monsters, not medieval-style closely-packed armies that are highly vulnerable to area effects.