Suppose a unicorn agreed to let a person ride/tame it for combat in battles, and assuming as a baseline, without any magic assistance, that the horn is made of a similar material to ivory, in the shape of a spiral, with a size range being a minimum of 12 inches and a maximum of 28 inches, how effective would its horn be in said frays? Particularly stabbing or lunging with the horn.

Edit: To add some clarification on what I mean when I say "combat" it as a baseline is against a small group of people that contains individuals both on and off horseback.

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    $\begingroup$ Is this horn wielded by the person? Or is it still attached to the unicorn? Who are the other combatants? Are they space marines encased in a ceramite suite of power armor, firing bolter rounds from an entrenched position? Or are they fish in a barrel? The effectiveness of any weapon is HIGHLY dependent upon the context in which it is wielded. Be sure to clarify if the combatants happen to be magically or innately immune to unicorn horns. $\endgroup$
    – sphennings
    Jul 22, 2021 at 2:07
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    $\begingroup$ VTC:ND, this Q needs more information to avoid the book test described in the help center. The horn would be useless against an Abrams M-1 tank, and that circumstance is not rejected by the question. It is unreasonable to leave the question so open. What technology level? What circumstances of combat? What are the configuration and disposition of both enemy and ally forces? Against my youngest niece a unicorn would be eminently useful. Just mentioning the word "unicorn" would turn her into an adoring friend. But I'm pretty sure that answer doesn't meet your needs in any way. $\endgroup$
    – JBH
    Jul 22, 2021 at 4:29
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    $\begingroup$ Horse-like creatures aren't really built for lunging the way a human fencer can. Can you describe what you mean by lunging when you edit. $\endgroup$ Jul 22, 2021 at 4:59
  • $\begingroup$ What kind of army do they need to face? If you could give us a time period (Neolithic, Bronze Age, Classical, Medieval, Modern, etc.) that could help inform the answer. Better yet would be if you could give a specific civilization to use as a baseline since a Roman Legion would poss a very different challenge than a Greek Phalanx or Persian Immortals even though they are all of roughly the same time period. $\endgroup$
    – Nosajimiki
    Jul 22, 2021 at 15:14
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    $\begingroup$ I hope we're all in agreement that unicorns don't have rules or properties since they don't exist... and treating them as a horse with a horn makes them less good than a horse and therefore, narratively also less good than a horse. So we need some kind of unique properties that make a unicorn special. Maybe they're vicious and their horns, heads and necks are extremely tough. Maybe they're extremely intelligent and skilled and can disarm most knights in one-on-one encounters. But I think unicorn = horse + horn is probably not great. $\endgroup$
    – anregen
    Jul 22, 2021 at 20:18

7 Answers 7


Not very in most circumstances.

Assuming a unicorn is is all other aspects (size, agility, endurance etc) identical to the average war horse and also assuming a pre-gunpowder setting I see the following problems;

Although the horn might be useful in and of itself an in a 'one on one' combat between two lone opponents where one is riding a normal horse (and the unicorn gets a chance to stab the other mount or rider) it will be of little use in massed combat.

Firstly just like a horse a unicorn has to get within range to use its horn and that means would it have to charge through missile range to get to the opposition. And since its just as vulnerable as any normal horse it will suffer similar losses doing so. (Remember also that in massed warfare the target is not any one horse or soldier. If you have 1000 horse in a formation (say 200 wide by 5 deep) charging 1000 archers (the same) each archer's target is one big mass of flesh that just happens to be 200 horses wide and 5 deep. Also generally the target was the horse not the man because well, the horse was bigger!

Then after you close to the enemy the reach of the horn is still less than that of your average armed opponent on horse or foot. Any pike/lance, pole arm, sword or mace etc has longer reach than the horn and again as far as the enemy is concerned the target is any unicorn within reach, so the first couple of ranks of spearmen for instance all have the choice of say 2 or 3 targets not just the unicorn immediately in front of them. And of course any three men can attack one horse if they chose.

Finally if they are identical to horses in all other ways then unicorns are not suicidal either and (unlike what you see in the movies) horses were historically not willing to charge blindly onto the end of a spear tip if they could at all avoid it! Which means they to would try to stay out of range of all those sharp pointy/stabbing things. Which of course again eliminates their horn as a option.

Where they might have an advantage would be in a more flowing, 'open' style of combat between small groups (think as an example skirmishes between the 'plain peoples' of 17th & 18th century North America) where a charging unicorn might be able to lower its head and take out an opponent if given the chance. Although again I assume the other side would soon learn to be wary of this tactic and would try to adapt.


They could easily be more of a detriment than a benefit

To prove this point, let's assume the best possible scenario for the materiel properties on that unicorn. We will say that it is hard and sharp enough to punch through armor and that the unicorn's skull and neck are properly reinforced to survive an impact at full charge.

Now let's compare that horn to the unicorn's other main natural weapon: its hooves. Horses are heavy, and when they impact an infantry formation at speed, only a small amount of the horse's inertia is required to punch a lance through an enemy's armor assuming you connect well enough to not just glance off... but all the rest of that energy could go into trampling enemy infantry. Because of the horse's size, each foot step the horse makes is like getting hit by a giant mace with enough energy to reliably maim or kill through armor, and a horse can have enough inertia to trample through several lines of infantry. In the Early Medieval period before long spears came back into fashion, when heavily cavalry would charge an infantry formation, the most important factor for success was having enough momentum to trample though the enemy formation and come out the other side. So, while the rider might take out 1 enemy with a spear, the horse might take out 4-5. For this reason, many cavalry though out history have actually preferred cutting swords like a spatha, saber, or falchion over spears so that they too harm multiple enemies on a single pass-by.

If you put a horn on the unicorn, it means that the first person you hit will get stuck on the front of the unicorn blinding it, weighing it down, and possibly still being alive long enough to have easy access to slit the unicorn's neck as you carry him along. Unlike a lance the unicorn can not just let go of his horn when it gets bound up in an enemy and keep moving. So, as a one-use weapon that only marginally improves reach, its ability to interfere with its multi-use weapons would make it worse than not having it.

How to make the horn a useful weapon?

First, it needs to be longer. The average cavalry spear (lance) throughout history was about 3 meters long which could reach about 1.5-2 meters in front of the horse. The lance would not necessarily do a ton of killing, but it could help break up the first line of infantry and press them back into the enemy formation enough to make defending against the trample much harder. So if your unicorn horns were about 3 times as long, they might be able to match the effectiveness of a lance.

Secondly, your unicorn needs to be able to "drop" it. Some animals have body parts that break off by design. Bee stingers, skink tails, etc. So, if you make it so that the horns are strong enough to impart significant energy, but them break off so they don't get stuck, then you could further replicate the utility of a lance.

The problem still exists that unicorns can not just recover thier horns after a battle, but may instead need to spend months or even years regrowing them; so, they are still not as good as a lance in this respect, but probably still good enough to be considered "useful".


During the London Bridge terrorist attack, a narwhal tusk was taken from a display case and used as a weapon against the terrorist. This is pretty similar to a Unicorn horn.


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    $\begingroup$ I think the OP was intending the horn to still be attached to a unicorn, not wielded by a human. We already know that long, pointed sticks and stick-like objects are effective weapons in the hands of a human attacker. $\endgroup$ Jul 22, 2021 at 19:05

Pretty useless.

A horse is not designed to charge head-first and head-down into things, regardless of whether the horse has a horn or not.
The horn will break or the unicorn will snap its own neck or both.

Even if the unicorn survives the initial impact he/she will at least be groggy or dazed from the blow and easily dealt with by the opposition.

It's a one-time use thing and will be pretty close to suicidal for the unicorn. I can see it happening as a last-resort option in a desperate situation, but not as anything that is usable/trainable for a real practical combat situation.

  • $\begingroup$ If you are a bit more open to your interpretation of "unicorn" and go with another animal that has been at times historically called a unicorn, the rhinoceros, it seems like charging into things is the point of the rhinocerouses horn. $\endgroup$ Jul 22, 2021 at 23:12
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    $\begingroup$ The rhino is not recognizable as a horse or unicorn though. A unicorn built like a rhino would be a rhino, not a unicorn. $\endgroup$
    – Alcamtar
    Jul 22, 2021 at 23:40

The mythological descriptions of unicorns vary somewhat between two different, yet similar themes. The similarities are that in both depictions, unicorns have a gracile, horse-like body plan with a roughly one to two metre long ivory horn projecting perpendicular to the head from between and just above the eyes. The differences are that some legends depict unicorns as being small, roughly human-sized creatures, while other legends depict horse-sized creatures.

Another point in the mythological depictions of unicorns is that they are very strong, easily capable of carrying a rider (even the small type) at a rapid pace. They were also said to be an even match for a lion in combat.

Finally, Narwhal tusks were thought in medieval Europe to be unicorn horns, so we can assume that unicorns will have horns with similar properties.

So... horses are cursorial mammals, adapted to running quickly, though due to these adaptations, they do not achieve their maximum speed particularly quickly, nor can they turn quickly in comparison to other animals which are adapted to using their horns as weapons against predators.

If we compare a horse with a horn-wielding herbivore which uses its horns in self defense - say, a Triceratops - we can see if we put the two animals on the same scale, that the Triceratops is far more robust and muscular than the horse, to allow it to lunge and turn rapidly.

So... naively, it would seem that unicorns, following a horse-like body plan, would not be particularly capable at lunging with their horns, that their horns (if they are as magical as they are said to be) are of use mainly as instruments of healing, not harming.

However, given that unicorns are said to be very strong, either their gracile, horse-like body plan is rather more robust than the legends suggest, or they are magically strong. While this strength may be used for the mythical purpose of carrying maidens for whatever purpose, it is also just the trait required to make them effective at lunging with their long, straight horns.

Of course, if unicorns are small, carrying a rider would effectively double the weight of their bodies, making them far less capable of lunging effectively (just try jumping while carrying another person your own weight). On the other hand, a rider may be around only a tenth of the weight of a horse or a large unicorn, and would hinder the unicorn's lunge far less. From the OP's description, this is probably the type of unicorn in question.

So... these cavalry unicorns would be capable of lunging effectively even while carrying a rider, and quite possibly while also wearing steel plate barding. Their horns, like the tusks of narwhals, should be strong enough to be used as spears, as narwhal horns have been done historically.

That the horns of the OP's unicorns are 12 to 28 inches (0.3 to 0.65m) long makes only a little difference... a sharp-pointed horn backed by the better part of three-quarters of a ton of muscle and bone should easily be able to punch a hole through medieval plate armour, and would inconvenience even a person in modern kevlar armour. Similar to a fencer, a lunge of 0.3 to 1 metre would be quite sufficient to inflict a fatal injury to an opponent, where a penetration of the chest cavity of under 0.1m could easily be fatal to a human.

Armouring a unicorn would make it quite a formidable opponent on the field of battle, though even medieval plate barding left significant amounts of the horse unprotected.

So, my conclusion is that yes, a unicorn could (given the assumptions I've stated here) be an effective combat-capable mount upon a medieval human battlefield.

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    $\begingroup$ Kevlar is significantly easier to pierce with a stabbing weapon than medieval plate-armor. Kevlar specializes at stopping fast, light, blunt weapons, not a slow, heavy, sharp ones. Kevlar vests that are rated as "slash" or "stab" resistant generally have an internal layer of light weight mail or brigantine that is only actually thick enough to stop a knife. Modern armor is not really designed around stopping spear thrusts or battle axes the way that plate mail was; so, the only way it would stop a unicorn if you fit it with steel/ceramic ballistic plates. $\endgroup$
    – Nosajimiki
    Jul 22, 2021 at 19:08
  • $\begingroup$ @Nosajimiki See also all those videos of Lockpicking Lawyer cutting apart "slash resistant bags" (some of which were made from Kevlar) with a pocket knife. $\endgroup$
    – nick012000
    Jul 23, 2021 at 13:05
  • $\begingroup$ @nick012000 Yeah well, everyone knows the only way to slow that guy down is with duct-tape. $\endgroup$
    – Nosajimiki
    Jul 23, 2021 at 19:49

All-in-all, this is your story in your world. Make these unicorns into your unicorns.

In a fantasy world with unicorns, as a player or reader, I would expect a fantasy element to unicorns. I would expect something that makes them very different from a horse with a horn. They must not be OP if you're putting them into a battle, (unless the point is for them to be the narrative cavalry that saves the day when all hope is lost).

My point is, I wouldn't be interested in a playing with or reading about a "realistic" unicorn that was defined on Stack Exchange. If I'm in your world, that's because its the world that you made, not because it's a world that closely matches realism. We like having some threads to reality that make things accessible and familiar, but we love the fantasy.

We want a wizard that studied weather control and can call down lighting. She may have to punch someone, but that mechanic isn't really a core aspect of the wizard. She can be a powerhouse and knock someone's teeth out, or she can be normal, or she can be frail and break her hand in the process. The story controls the mechanics. We want unicorns that can heal, or maybe if their horn is broken off, the unicorn becomes an untethered bolt of chaotic energy.

If your world doesn't have established "unicorn rules" that your players/readers would expect to be followed, this is a place where the "baseline" can be mostly irrelevant. I'm not saying "it's pointless", I'm saying don't sweat it. You can make that any mechanic that fits the story. Maybe just take whatever you use for a spear and give this creature approximately the same capability. But as a consumer of this story, I would feel a little jilted if the unicorn's most significant contribution is being a horse with a horn. And if this universe has unicorns that aren't magical/special, then I still think you're the best person to decide what that unicorn is.

  • $\begingroup$ You can read my other response for what was intended to be a more comical way of presenting the same idea about mechanics serving your world and story, rather than the other way around. worldbuilding.stackexchange.com/a/207617/86142 $\endgroup$
    – anregen
    Dec 22, 2021 at 19:58

A unicorn ridden by a person is the most powerful weapon in your universe.

Note: I assume we're talking about a mer-person rider since they are most common and "humans" do not exist as such in this universe

Since assailants can not look directly at the mer-person (because of their tardis-perception-filter-like properties) they are difficult to even acknowledge as an adversary. Also, the time-skipping movement of the unicorn makes them extremely agile as well as hard to target or understand where precisely they are going. The combined charismatic influence of the two would turn some immediately into loyal followers (almost worshiped), but even the ones that aren't fully affected would be unable to consider the pair as a traditional "enemy". Since the touch of mer-people can make an animal invulnerable to wood, metal or stone, and the breath of the unicorn can make itself and its rider become ethereal at will, most weapons are useless against this duo! Additionally, they are equally effective units traveling on land, through water or even into the skies (assuming of course that the unicorn is shod with the standard hard-light shoes that are common in this setting)

OR it's possible that none of this fits into your universe and you could make up literally anything.


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