Can Wall of Stone be cast on dirt?

Question

The spell description for Wall of Stone states:

It must, however, merge with and be solidly supported by existing stone.

My group was adventuring on a plain, where the ground was made of dirt. Presumably there was rock below us somewhere, but we didn't really have any way of knowing exactly how far down that was. We were trying to make a shelter using the spells that we had, and Wall of Stone looked good, except for that one line.

Our GM ended up houseruling that as long as the structure could generally support itself, it didn't need to actually merge with stone, but I'm interested to know how other people would handle it.

In your game, do you require Wall of Stone to merge with existing stone, as the spell description states? Do you allow walls to be created on dirt, wood, or other materials? Am I just reading this description wrong?

Answer 1

The example given in the spell specifies that "dirt" is ok. I feel as though this line is being taken out of the context it's written in. Here is the full context.

The wall doesn't need to be vertical, or rest on any firm foundation. It must, however, merge with and be solidly supported by existing stone. Thus, you can use this spell to bridge a chasm or create a ramp. If you create a span greater than 20 feet in length, you must halve the size of each panel to create supports. You can crudely shape the wall to create crenelations, battlements, and so on.

As long as the stone wall is merged with and coming out of a stone from which the wall can be made, it seems that are ok. I can't imagine that there exists a chasm which is pure stone without dirt, from which the spell is describing when it says you can create a ramp or bridge out of the wall.

As an evocation rather than a conjuration spell, it makes sense that the wall might require some stone to work with. This has been confirmed by Mike Mearls, that some sort of rock is required:

‏@wax_eagle : @mikemearls Can Wall of Stone be cast on dirt? It seems like its written to always need stone to merge to. Is that correct?

Mike Mearls : @wax_eagle that's correct - need some stone to merge with or be supported by. for instance, a bridge is OK if the two ends touch stone.

Daganev : @mikemearls @wax_eagle So no stone walls on a grassy knoll?

Mike Mearls :@Daganev @wax_eagle Correct, you'd need rocks of some sort (ruins, boulders) to support it.

Answer 2

The wall doesn't need to be vertical or rest on any firm foundation. It must however, merge with and be solidly supported by existing stone. Thus, you can use this spell to bridge a chasm or create a ramp.

A correct interpretation here requires parsing whether or not the first two sentences in this paragraph are related at all. It is clear that they are related. The "however" in the second sentence is a contradiction of the first.

The problem though is that it's not an exclusive contradiction. That is to say, it's not:

if you don't have a firm foundation you have to have stone to merge it with

It's this:

You have to have stone to merge it with.

I think this can be a read as the first statement, and if I was guessing at the intent, I would hazard that this was the intended version of the rules.

However, as the spell is written, I believe that any casting of it requires solid stone for at least one panel to merge into. For a bridge, both ends must merge.

Mike Mearls has confirmed that you must have stone to merge onto it:

Mike Mearls: that's correct - need some stone to merge with or be supported by. for instance, a bridge is OK if the two ends touch stone.

daganev: @mikemearls @wax_eagle So no stone walls on a grassy knoll?

Mike Mearls: @Daganev @wax_eagle Correct, you'd need rocks of some sort (ruins, boulders) to support it.

Answer 3

The RAW is clear. Unless I had a good reason to houserule, I would use it as written. I.e. allow it only when the floor or supporting walls are stone.

A good reason might be a campaign that almost never has enough stone for it. For example, one that took place primarily in a forest and had no suitable dungeons either. In an underwater campaign it would be reasonable to refluff it as a wall of coral, although it could also be usable as written.

However, even in such a case I'd be more likely to just guide the players towards other spells. Only if it was somehow important for a character concept would there be a reason to do otherwise.

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Apparently not everyone agrees that the RAW is clear, so here's my rationale for it. This is the whole relevant paragraph, from beginning to end:

The wall can have any shape you desire, though it can't occupy the same space as a creature or object. The wall doesn't need to be vertical, or rest on any firm foundation. It must, however, merge with and be solidly supported by existing stone. Thus, you can use this spell to bridge a chasm or create a ramp.

So four statements here.

The first tells it can be shaped, but also limits it from occupying an object. The second gives more specifics: no need to be vertical, doesn't have to rest on the floor. The third again limits it to merging with stone for support. The last statement is just an example to illustrate what the earlier ones imply.

There is nothing there to imply that the third somehow only matters if you shape the wall specially. Instead, these are all rules about how you can use the spell, all must be followed. If you read it like that, there is no contradiction, so it's the natural way to read it.

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Update: from wax_eagle's comment, a tweet from Mearls confirming that it must indeed be supported by stone.

Answer 4

Not sure if this needs to be answered or just commented on but I would rule that as long as the ground underneath the stone wall could support the final weight of the said structure the spell would complete with the magic forming the stone out of the ground thus their would now be stone under the wall. As with most earth magic it comes from the earth thus if its dust, dirt, rock, gravel, stone or sand its all "stone" in smaller bits.

Answer 5

The RAW is clear. You need a foundation of solid stone. I think the RAI is that there should be no impossible constructs. You can construct a wall that is flat on the gound and protudes into the void like a spring board and you will need a solid foundation for it. This cannot be anchored with a piece of fluffy grass, it would never work with a non-magical wall.

Personally, I think the RAI makes sense, but the constraint is placed on all walls and that's a too heavy constraint for a level 5 spell. I'd keep the constraint for walls that could not support themselves if they were build non-magical, but drop it for any wall that could have been build by a mason. If the wizard decides he wants to build an L-shaped wall that supports itself on a ground that can support the weight of the wall, I'd be fine with it as a GM and don't care for the ground material.

Answer 6

The rules are pretty clear that it must be on stone if you go RAW, BUUUT, the DM could handwave that by saying that the dirt in that particular area was packed hard enough that it behaved like stone. If the idea was presented in a game I was dm'ing, I'd allow it, but I'm kinda new to DM'ing, so.. Take that with the customary grain of salt.