If you want to avoid those Finesse rolls, just create a massive plank of wood to span the 30 pace gap in the bridge. Think of it as putting down a 2x4 to get across... except much larger. So what you want is, say, a plank 40 paces long (an extra 5 paces on each end for support), 3 paces wide, and 6 inches think. This works out to 20 cubic paces of wood.
CrHe Base 2 gives us a processed plant product, such as a plank of wood. Perfect!
Base 2, +1 Size (10 cubic yards) +1 Touch, +1 Diameter = CrHe 5. Cast this twice for two planks side-by-side so you can get the cart and horse across.
Or Base 2, +2 Size (100 cubic yards), +1 Touch, +1 Diameter = CrHe 10 size if you don't want to cast it twice.
Either way, the Finesse roll to lay down this massive plank to span the broken halves of the bridge would be significantly lower than trying to create a bridge. You don't need a fancy bridge, just a way to get across -- and most of the bridge is still there.
Sorry. It's very nice, but you do kinda need atleast parts of the fancy bridge: the supports.
a 100' plank isn't going to stay straight with even a minimal amount of weight on it.
At only 6 inches thick, it'll bend and probably break.
I'll leave it to the engineers to give you the details.
A 6" thick piece of oak is an extremely stout piece able to withstand a lot of bending force. I invite you to try and break a 6 inch piece of oak. It's not as easy as you propose.
Create a barge made of wood, large enough to carry you, your cart and your grog accross the river. This is a CrHe 15 spell (Base 3, +1 Touch, +2 Sun, +1 for Size). Some may argue that another magnitude for increased size is needed. But the canonical Bridge of Wood uses +2 for Size and create a bridge that's 5 paces wide by 20 paces long,so I don't think that would be needed for a much smaller barge.
Use a second spell to control the barge's movement across the river. This is a simple ReHe 10 spell (Base 3, +1 Touch, +1 Conc, +1 Size), though some might again argue that it may require an additional magnitude for even more size, or for stronger control due to the strength of the current. That would still leave this a level 15 spell.
EDIT: If you're not good ar Herbam, you might do the same using another Form, such as Aquam (for an ice barge) or perhaps even Animal (hide and bone).
So double the depth and you halve the width. Conjure oak (or some other strong wood) instead of pine. You have to cast several time to get enough 40 yard planks to get a sufficient width. The point is to show you can do it with a 1st (or 2nd) magnitude spell, which can be sponted even by starting magi "in a reasonable amount of time" (per the original post).
Hmm. Touch (R:Touch +1) the chunk of dirt your all on (T:Part +1, Size +0) then quickly (D: Diameter +1) float it across the river. (ReTe Base 3;Unnatural Movement). That's a single ReTe base 10 (3+1+1=5, 5+1=10) with no need for a finesse.
Can't find this gyro-stabilized lance...
The closest canonical spell I can find is actually in The Lion and the Lily, The Unerring Lance and it is a ReTe spell with Base 5.
Building a bridge across a swift river (100 yards across) is not going to be an Easy (craft roll 6) task for a Craftsman. Remember that an Easy task could be completed by the most amateur (Craft 1) of craftsmen roughly 50% of the time. There are probably only a handful of bridges in Mythic Europe that would come close to this span (if any) - because this is hard stuff to do. Any magus who could do this with Craft Magic would be hailed as the greatest Finesse master ever, really. Assuming Finesse 10 (Craft Magic Specialization), +5 Stat, Puissant Finesse, buckets of Precise Casting Spell Mastery (say 3 ranks) and a Craft Skill of 5+ associated, you can get a Finesse total before roll of 24. It can be done by dedicated masters, but not dilettantes.
Having played a Craft Magic Magus through 30+ years, I can say that it's a hard road to follow. You can't expect to be good at many craft skill simulations because the difficulties are high once the time and associated craft skill knowledge is taken into consideration. You either settle for quickly and crudely made everything or a few things you can make nicely. Relevant rules are in Covenants and HoH: Societas (Jerbiton). And Art and Academe basically makes Craft Magic art even harder/crappier. Seriously, magi weren't competing with artists effectively anyways, there was no need for the hit.
As a side note, the Inca were making rope bridges that were this order of length for centuries past. Made of locally sourced grass and the labor of a few hundred folks. Seriously amazing stuff, though it wouldn't support a horse and cart (but neither would the mountain paths they connected).
It's a pretty big span, at least in terms of Hermetic Magic. With regards to Craft Magic, the things to consider are the number of craftsmen necessary to build the bridge, the skill of the craftsmen and how long it takes them to do it, because all those things factor into how much finesse is required for craft magic. Like John said, a magus pursuing this will probably have a pretty high finesse score and is pretty specialized (something I suggested with respect to Arts, but I was thinking it fit for Finesse, too).
The span is difficult for a Hermetic Magus to do quickly and accomplish all three things, because almost all of the effects are around 20th level, which suggests TeFo scores in the 35+ range to make it a reasonable shot at success, and even then, it will require the magus to stretch himself.
Aren't you making a single spell do multiple effects here? Namely, making it move over a surface (water) and remaining coherent/hard enough to carry your cart. I'd probably require at least an additional magnitude for the inherent difficulty of the task. Or use a Muto requisite to give the dirt the ability to float, but that effect is a MuTe 4 guideline...
Furthermore, if we look at another spell that uses the same guideline, The Unseen Porter, the speed of movement seems to be slow when trying to move large/heavier objects. So I doubt whether the movement would be fast enough to allow the patch of dirt to make it to the other side in a mere 2 minutes. So you'd either have to risk a Concentration roll or boost your duration to Sun by adding a magnitude.
But it's a nice idea. It's just more along the lines of a level 20 effect, rather than level 10 as you suggest. IMHO.
When on an expedition (particularly if moving with an entire cartload of stuff) the grogs of our covenant always make sure they have basic equipment like stuff to make a fire, blankets, one or more shovels etc. One of the things they are never without is rope; in particular, the "standard" equipment for an expedition always includes at least one rope of stout silk (and possibly more if the expedition is large), about 100 paces long and 3/4 of an inch thick (it can hold half a dozen tons of weight): useful for tethering horses, climbing, lifting/dragging/tying stuff etc.
In this case, the rope could be used to solve the problem with a single Level 3 spell.
Have the grog tie it up around the cart and the horse (detached from the cart) as if one planned to lift both cart and horse aboard a ship by means of a crane. Have the magus and the grog stand on top of the cart, with the magus touching the rope. The magus then casts a R: Touch, D: Conc, T: Ind Rego Animal spell using the Base 1 guideline "Manipulate an item made of animal products" on the rope (+1 Touch, +1 Conc). This spell simply "picks up" one endpoint of the rope as the hook of a crane would, and gently moves it (with the attached load) to the other side of the river.
Second, Hard (12) is only hard, not impossible. By City and Guild, a workshop total of 12 is required to make Superior Items, one grade above Standard Items (which require a 6). Short bridges might be easy-average, but 100 yards of bridge over a fast river is never going to be easy. It's going to be done by a master architect with a legion of stonemasons. It's not as fancy as a cathedral, but I'd expect Cathedrals to be Excellent Items (Workshop 15), given that they are the gold standard for stonework.
I vehemently disagree with this. At best the spell could be used to tie itself around the rope, but I doubt that the spell provides enough force to pull a wagon.
Let me ask you (Tellus and jonathan.link): would you allow the Base 1 guideline to be used for the classic "rope trick" that affixes one extremity of a rope to a point in space, and holds it there with as much force as needed to break the rope? In our saga it's a standard, often used effect. If you don't, what guideline would you use for it? If you do, would you allow a version where the extremity is not affixed to a point, but to a plane (e.g. it's affixed at a given height, but you can move it around)? If so, the effect described above can work with little modification.
