How to transport armies across Faerûn?

Question

Is there a way to quickly move thousands of units? In general, or for a specific case in Tyranny of Dragons?

I looked at:

• the Gate (9th) spell, but it last only 1 minute, so not really feasible; I'd have to claim each city had tens of high-level casters to do it. It can only open to another plane so they'd need to stage somewhere else. (Perhaps the ethereal plane near the destination if there's a way to get people from the ethereal to the prime material more easily than planar travel in general.)
• Teleport (7th), limited to 9 creatures
• Teleportation Circle (5th), requires a permanent destination teleportation circle. So at most, armies could get to Baldur's Gate for the case I'm considering.
• Treestride (5th), range of self, nearby tree within 500 ft allowing very fast movement through a forest for the caster for one minute. [editor's note, did you mean Transport Via Plants (6th) which turns a large plant into a portal for 1 round that people can run through? Critical Role frequently mis-names it as Treestride.]

Any other way within the rules to accomplish such a feat?

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The specifics are spoilerish for Tyranny of Dragons

I'm nearing the end of the module.
I want the armies of all factions to reach the Well of Dragons, where the final battle ensues.
If there isn't general-purpose army-moving magic, I have to say they all get to Baldur's Gate, sail until Elturel, and walk the rest of the way. Doable, but not that epic.

Answer 1

Who needs magic?

You say they'd need to sail to Elturel then march the (quite considerable) distance from there to the Well of Dragons. But the River Chionthar (that flows past Elturel down to Baldur's Gate) continues east for quite a while. If you keep following it upriver, then switch to the River Reaching at Scornubel, where it flows into the Chionthar, and follow it on, through the Reaching Woods and Skull Gorge, you eventually end up very close to the Well of Dragons:

So you don't need slow exhausting marches, just keep sailing on from Elturel for as long as the river remains navigable (it's definitely navigable through to Elturel, I don't know if any source materials specify how much further it remains navigable).

But I want magic!

This strategy works just fine with magic too, and magic makes it more reliable, quicker, and less tiring than the other options. A single casting of Control Weather lasts up to eight hours, and continually operates in a five mile radius around the caster. Make up a fleet of troop transport ships, have just one 15th (or higher) level cleric, druid or wizard per 10 mile long segment of the river, and they can reliably use sails to travel upriver. If you have three such casters (and magical or nonmagical light to minimize the risk of running aground at night), they can make progress 24/7 (well, 24/10 I guess, what with FR having tendays, not weeks).

Lower level casters (Druids, Sorcerers and Wizards) can contribute a bit as well, at 9th level, when they gain access to the 5th level, one hour long Control Winds that offers the same benefits, just for a shorter period and a smaller area (just a 100' cube), so it could move a few small ships or a couple larger ships at most.

Without high level casters, the very rare Anstruth Harp or the legendary Ollamh Harp can both be used by an attuned bard to cast Control Weather once a day, so if some of the armies involved have access to powerful magic items, much weaker casters can be used to achieve the same effect.

Answer 2

A well of many worlds can do it if you want

The well of many worlds is a magic item that says

[...] It unfolds into a circular sheet 6 feet in diameter.

You can use an action to unfold and place the well of many worlds on a solid surface, whereupon it creates a two-way portal to another world or plane of existence. Each time the item opens a portal, the DM decides where it leads. You can use an action to close an open portal by taking hold of the edges of the cloth and folding it up. Once well of many worlds has opened a portal, it can't do so again for 1d8 hours.

You would need to use it twice: one time to move the army to a staging ground anywhere on another plane. The second time, 1-8 hours later, to open a gate near the well of dragons, which you as the DM can decide opens there.

If there is concern about the choice of location, you can have magical research show that there is a natural affinity for the well of many worlds to open the portal at the Well of Dragons. After all, there is already some kind of interplanar connection there, with Tiamat's temple having been pulled from Avernus (Rise of Tiamat, p. 171):

The temple in the caldera of the Well of Dragons is the same temple that marks the center of Tiamat's realm on Avernus.

The size of the portal may be an issue though: large war machines would need to be taken apart to pass through, and large or huge creatures may need to be polymorphed or reduced first. That’s probably not beyond reach for an army with access to legendary items.

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PS. As for any answer with an how-to, here's the obligatory wish paragraph: a faction of course also can use an off-label wish to move the entire army somewhere. You as the DM get to decide if that works or not.

Answer 3

You left out Transport Via Plants (6th) to make a portal or gateway for a round. And strangely you included a self-only short-range movement spell, Tree Stride (5th). It lets the caster spend 5ft of movement to step between similar-type trees within 500 ft, duration 1 minute, allowing very fast movement through a forest, but no more useful for armies than Dimension Door. Perhaps an actual-play show has you mixed up? Critical Role players often said "tree stride" when they were talking about Transport Via Plants.

Transport via Plants (6th)
1 action, duration: 1 round. classes: Druid

This spell creates a magical link between a Large or larger inanimate plant within range and another plant, at any distance, on the same plane of existence. You must have seen or touched the destination plant at least once before. For the duration, any creature can step into the target plant and exit from the destination plant by using 5 feet of movement.

A tree is the standard choice, but a large enough kelp frond underwater could work. Perhaps a large-enough patch of moss, allowing a larger area transport? Or a very large-diameter tree, or a recently-fallen tree that has many adjacent squares for a whole column of troops to run through with readied movement + their turn to move+dash.

Narratively, some tables such as Critical Role describe Transport Via Plants as opening a literal portal / passage in one side of the tree. The spell description just says "step into the target plant", which can include people standing on tree branches, and exit from anywhere on the destination plant. It matters whether people can move into the tree from any adjacent space or only from ones adjacent to a specific point, for big trees or other plants that occupy many squares. (Does a Large size-category plant include a shrub that's 10 feet tall and round? What about a young tree that's only 10 to 15 feet tall with a trunk you can wrap two hands around?)

Applying D&D turn and movement mechanics, Transport Via Plants can let everyone within sprinting distance (like maybe a 40 to 45 foot sphere) run through on their turn without causing a traffic jam. Every creature has their own turn and passing through the same space during separate turns doesn't create a conflict in 5e mechanics, only where they end their turn matters.

But narratively it's a lot of people sprinting toward the middle of a circle, which will create crowding even before they reach the tree. And if you treat it as creating a narrowish portal, that's a 1-square-wide choke-point for everyone to pass through in 6 seconds. Stuffing this many people through it makes me think of fluid dynamics and Bernoulli's principle.

D&D isn't a physics simulator, so when you encounter a situation that doesn't make physical sense but which is allowed by the turn-based model, it's up to the DM to decide whether it works. I'm very clearly and intentionally exploiting D&D's narratively-overlapping-but-mechanically-sequential turn mechanics to get more people through a small space in a limited time than I know could actually fit.

That said, some ways to get the most out of one casting of TVP might apply whether or not you impose extra limits on having large crowds move into / through the same spaces (especially if TVP at your table creates a 1-wide passage, rather than allowing stepping into the plant from any direction).

Scaffolding for a couple levels of vertical packing at the source. Extra people close to the tree on the source side can get farther from it on the destination side, and area increases with the square of distance, so 2D spreading should be fine on the destination side.

The people who started far away on the source side have a problem, though: the ring of people 45 to 55 feet away won't will only have 10 to 0 feet of movement left after reaching the tree and using 5 feet of movement to step through it. So that's a problem unless you have some localized spread-out effect or something that shunts people to the nearest unoccupied space (which TVP does not do on its own).

TODO: count squares in that radius on a grid.

Arcane Gate (6th) on either or both sides can put more squares within movement range of a plant, if you have that to spare from arcane casters. It's a local 500-ft-range two-way portal.

Answer 4

You can fit a hundreds or thousands of people through a single Teleportation Circle or a Gate.

Far more than I feel you're giving credit, as long as it's a planned move and not an, "Oh crap, quick, everyone get through the portal before the volcano erupts!"

Your premise includes armies, which I've taken the liberty of assuming have some form of martial discipline and a chain of command they follow, so organizational efforts are a given.

In combat/initiative, you can only have one medium or small creature in a square at the end of a turn unless size exceptions- but this is not nearly as restrictive as it seems at first glance.

In these circumstances, in a 50 foot square (10x10 5 foot squares), you can fit 100 individuals. We'll assume all the heavy armor wearers have 15 strength. The mage opens the portal at the middle of the square, and no one has to have more than 25 feet of movement to get in.

This means we can double it to a 100 foot square (20x20 5 foot squares) and require them all to double-time it to 50 feet in six seconds, which fits 400 people, and with an army lined up to go through in organized ranks as soon as the portal opens, all of them getting through in six seconds is simply a matter of marching discipline- they don't have to stop moving when they get to the other side of the Circle or Gate, and can continue to file through into rank formation to make room for the next wave.

With a Gate lasting a minute and an organized army filing through double-time in ranks, you can multiply this number by 10, and now you've transported 4000 individuals.

You can also include two extra ranks of medium/light armored units between 55 and 60 feet away, and horse-mounted cavalry can ride through the Circle or Gate from even farther away, multiplying your potential numbers even higher.

Out of combat, creatures can share space.

Some measure of common sense will apply, but this allows you to multiply the above figures even further- so unless each army is multiples of tens of thousands, one or two such casters per army should do the trick just fine; and at numbers of that size, having four such casters wouldn't necessarily skew the population too badly, still coming in under .05% of the total population of an army, where you expect the combat monsters to be located.

Answer 5

Cooperative Demiplane(s) - Capacity limited only by number of available high level casters

I know my other answer said you don't need magic, but I just thought of a viable means of transporting an essentially unbounded number of troops from point A to point B without relying too much on mechanical hacks to optimize the per-round movement rules. It requires at least one 15th level Wizard (or a 13th level Thief with various scrolls to fake it), plus your choice of:

1. One 15th level Wizard or Warlock (guaranteed success, no expensive resource cost)
2. A 13th level Thief (guaranteed success, but entails cost of scribing a scroll)
3. A supply of lower level Wizards or Warlocks with high enough stats, Helping each other to read a scroll outside their normal casting range (no guaranteed success, might require multiple scrolls)

The approach is this:

1. 15th level Wizard casts Demiplane, making a demiplane with an open door
2. They take the allied casters through to the demiplane, show them around, familiarizing them with the nature and contents of the demiplane (alternatively, if the demiplane was created before, they can provide this information without actually casting Demiplane, since the spell doesn't actually require visiting the demiplane to access it)
3. When it comes time to move an army to an arbitrary location, the 15th level Wizard uses Teleport (for intraplanar travel), Plane Shift+Teleport (for interplanar travel, though since they're both 7th level spells, this requires some time to rest in-between, and therefore coordinating the timing carefully), or if they're 17th level or higher, Gate (for maximum accuracy and speed for interplanar travel) to transport them to the target location.
4. Their ally still with the army in the original location either casts Demiplane normally, or if they're not a high enough level spellcaster, casts it using a scroll. Either way, rather than targeting their own personal demiplane, they use the alternate effect:

   If you know the nature and contents of a demiplane created by a casting of this spell by another creature, you can have the shadowy door connect to its demiplane instead.

5. The 15th level Wizard casts Demiplane, opening a door to their personal demiplane in the target location.
6. You now have two doors into a 30'x30'x30' demiplane, one connected to the location of the army, one to their destination. Both of them can admit Medium-sized creatures, both of them last for an hour.

As a conservative estimate, with no shenanigans like people spreading around the door and timing their actions to charge through one after another with unbelievably coordinated timing, a single-file column of soldiers, one every 5', traveling at Fast Marching speed, could directly march 4224 soldiers through in an hour (basically, the back of the line would be 4224 * 5 feet = 21120 feet = 4 miles from the portal, and the soldier at the end of the line would be fast marching four miles/hour to pass through the portal just before they close). If the DM allows multiple files of soldiers to zipper pull through the doorway, or for soldiers to share space out of combat, you could easily have at least five columns of soldiers (or more, maybe 10 columns, if you're allowing them to Dash to speed movement for the important portal transition), with two soldiers sharing each 5' square, bringing the total to somewhere between 21120-84480 soldiers in one hour.

And of course, if you have additional high level casters, or multiple days to prepare, you can multiply the effects. A single casting of Teleport or Gate or the like transports half the casters to the target directly, then, working in pairs with the other half at the army's location, they can each open these paired demiplane portals, scaling the total number of troops who can be transported linearly with the number of casters. Got 10 folks with the necessary abilities rather than two? You can move five times as many troops. Got a few days before the deadline? Repeat this trick daily at a coordinated time until they're all there.