How can infantry and light cavalry defeat heavy cavalry in a valley?

Question

At the climax of my medieval low-fantasy novel the protagonist has to besiege a castle that (from his side) can only be accessed through a valley. The valley is quite cramped, and the hills are too tall and steep for any horses or heavily armoured men to climb without great difficulty. The fight also takes place during the winter, adding shin-high snow as well as strong winds into the mix.

The problem is, the valley is guarded by a small group of heavy cavalry (supported by a small force of infantry). The protagonist has superior forces, but they mostly consist of infantry and light cavalry.

The enemy cavalry have both lances and swords. The infantry are mostly pikemen, with some archers. The hero's cavalry mostly carry shields and spears, while some have shields and swords. About one third of the infantry are archers, while the rest have pole arms or swords. The hero also has some engineers and sappers, but limited siege equipment.

Both sides have mostly veterans in their armies, but the hero's troops have excellent morale, compared to the somewhat average morale of the enemy.

If the protagonist does not succeed to capture the castle within a few days, the bulk of the enemy's somewhat superior army will arrive and reinforce the fort, easily routing the hero's troops. If the hero captures the castle, they will have little trouble holding off the enemy, as the terrain is mirrored on the other side, as well as there being a slope downwards from the castle.

My original idea was for the protagonist's troops to somehow draw out the troops from the valley, so that they could surround them and cut off any eventual retreat to the keep. Due to the time constraint, the hero cannot afford a long lasting siege.

I have little knowledge of medieval strategy, but I do not want the hero's "plot armour" to save the day. How can the hero realistically beat the enemy troops holding the valley? Also, is this concept somewhat plausible, or should I scrap it for a better idea?

Answer 1

There are really too many variables here, but I can cover some basics, maybe it helps?

Infantry versus heavy cavalry usually comes down to cavalry charge and the result depends on whether the infantry breaks under charge or not. Typically the cavalry would also try to flank the infantry, but with terrain described as a valley and the attacker having more light cavalry we can probably assume that won't happen here, so it is all about being able to withstand a charge.

The absolute requirement is for the infantry to have good discipline and morale. Professional or otherwise veteran troops are recommended. Being charged by heavy cavalry is very scary and liable to cause contagious panic. Panic will break formation and if your formation breaks under cavalry charge that is game over.

Morale implies competent leaders and a cause that the soldiers can at least relate to. Or just good pay and belief in victory.

Second is having suitable equipment that you can use to receive a charge and training to use it properly in formation. Typically this would mean pikes, but halberds and similar polearms also work. Heavy infantry with superior discipline can do it with normal spears, shields and armor. But we are talking about Roman legionnaires or Greek hoplites with solid leadership here, medieval infantry just was not good enough due to heavy cavalry being dominant at the time. So pikes or polearms would be my recommendation.

Missile weapons add a variable too. Archers with long or composite bows can stop heavy cavalry charging uphill, if they have some heavy infantry for protection. Similarly mounted archers are reasonably effective against heavy cavalry, if they have some heavy infantry for protection or a wide plain to run around. In your case maybe make the light cavalry archers and have them whittle down the heavy cavalry and enemy infantry.

Some heavy cavalry actually carried bows, which might add some difficulty and flavour to the fight. And some heavy infantry carried darts or throwing spears to break enemy formation when they charge.

Also you can use obstacle to slow down the cavalry charge which has great value. Using terrain to make cavalry charge uphill was already mentioned. You can also use caltrops or, if you have time to prepare light field fortifications such as palisades or ditches. Again medieval infantry generally was not good enough to build and use field fortifications during battle, but if the general decides to advance slow and methodical up the valley, field fortifications could be used to protect troops from counter-attacks..

And field fortifications would be very valuable, if you can build some behind the enemy... Bottling them up between fortified position and advancing force in a valley is pretty much only way infantry can trap cavalry actually. So camping in front of the valley while using light cavalry for scouting and screening, sneaking part of your infantry and some sappers behind the enemy force drawn forward by your encampment, building a fortified position manned with the infantry and some dismounted mounted archers, and then advancing into the valley with the main force might fit your needs.

This seems to fit well with the information provided in the comments. A long and fairly narrow valley would constrain the movements of heavy cavalry. And if the enemy would be drawn forward there would be cramped locations behind him to fortify and hold. The mountains on the sides would provide cover for the movements of the encircling force. If the mountains are difficult enough for heavy cavalry the enemy commander might not even be aware that infantry and cavalry scouts can get behind him.

Also the arrogant personality given for the enemy commander is significant. An arrogant commander would not worry about being encircled and trapped before he actually has some reason to think the enemy can get behind him. Arrogant people are also much easier to draw forward. To some extent a leader like this would find it very difficult to stay in the fort, if it seems he could position his forces safely far forward. I mean your infantry can't outrun his cavalry, so he can always make safe fighting retreat back to fort, right?

I propose that since he is apparently not only famous, but also a person who values his reputation as a fighter, you can simply insult him. Camp your infantry at the other end of the valley, there they block the valley, but are safe from attacks from the fort. Then send your light cavalry up the valley to do some casual looting, hit-and-run attacks on scouts, and sing insulting song about "the old coward who hides in his fort (probably under a maids bed)". Cavalry hates being trapped inside forts anyway, so he should be drawn forward as long as you make it look safe.

You can also simply invite him for a cup of tea or game of chess. Refusing would make him look like a coward. And while dropping by to drink tea and play chess doesn't requiring taking all his cavalry for escort, it would raise some perfectly valid looking questions about why the heavy cavalry is hanging back at the fort when they could be protecting the valley leading to the fort and positioned, at least in theory. to take the fight to the enemy. (And if he is famous, he might have nice stories.)

Answer 2

I'm assuming that the castle is uphill from the hero's forces.

The only real choice the heavy cavalry has is to charge the hero's army, and with good reason too, the charge downhill will be that much more devastating as the riders will keep momentum much more easily as they clash into the hero's ranks. This, however, can be used to the hero's advantage.

Consider the following formation:

As it is right now, the hero is bound to lose. But now imagine that the front line infantry have hidden long pikes in the ground just waiting for the cavalry to charge.

It doesn't matter if the riders notice it during the charge, their momentum and the slope will make it near impossible for them to stop, essentially impaling themselves into the pikes of the hero's infantry.

Even if the cavalry manages to stop they are now at a disadvantage because they are stopped, outside of the support of the fortress, with arrows raining on top of them and infantry and cavalry marching towards them, they've just lost the battle. They can retreat, but there's not much use for cavalry inside a castle, meaning they're now just infantry.

Now, why would the enemy's forces decide to let their infantry inside the walls? because that's where they'll be more effective. You see, the purpose of a fortification is to increase the defensive and offensive capabilities of your forces by sacrificing their mobility. For example, the siege of Corfe castle in England was won by the defenders, who only had 5 soldiers, against a force 500. That is a 1 to 100 difference in strength.

So, the biggest threat for your hero isn't really the heavy cavalry, but the actual siege, especially since your hero doesn't have siege engines. His best bet would be to simply cut off the fortification and starve its soldiers, but the enemy has a bigger force marching there, so it's not really an option.

You could have the hero build a counter fortification to protect his siege, this way, the same that applies for the forces inside the castle against his applies for his forces against the enemy's marching army, with the exception that the hero's forces would only be cut off from one side.

Answer 3

If I were in the hero's boots (or mocassins, or shoes, or whatever), then I would definitely NOT order a night assault, and I would rather not rely on my pikes to stop the charge of heavy cavalry - despite the incline forcing them upon my spears, I would wager experienced heavy calvary would have too much discipline to commit the cardinal error of cavalry - charging massed pike. Moreover, because of their defensive disposition, they have no compunction whatsoever to sally forth from their castle; they can just sit tight for a few days and auto-win. Short some VERY bad decision-making on the part of the defenders, you're not going to be able to rely on them making a wild charge for your lines.

That being said, assaulting the enemy's keep with all of them inside sounds like a recipe for heavy casualties, as usual - something most heroes would like to avoid, especially since it doesn't sound like he enjoys overwhelming numerical superiority. Short the time to build siege weaponry and batter the walls down, he'd have to throw ropes or ladders over the walls to get up - dicey business at the best of times; basically you try to throw up more of them than the enemy can cut down in order to get some guys on top.

That all being said... you have engineers, sappers, and the snow on your side, and I propose to use them ALL in order to force the issue on the field of battle. What follows is a step-by-step, foolproof plan for taking down this castle:

1. Under cover of darkness on the first night, your engineers, sappers, and volunteers painstakingly construct a snow-tunnel leading up to the enemy's walls while the rest of the army pretends to begin constructing siege equipment by the light of their fires.

2. At the wall, your engineers and sappers begin mining a tunnel under the wall to collapse it - to speed the process, they can even try to melt snow by fire, let that meltwater run into cracks in the foundation, and then bellows can be employed to blow icy air onto the cracks, fast-freezing them and breaking apart the base of the wall.

3. At some point, the enemy may discover their walls are being mined; they will be compelled to sally forth in order to drive off the sappers - this is actually the best possible result, because then your hero's army can defeat them in the field with massed archery fire (it sounds like you have more archers than the enemy) and the harrying of light cavalry to keep them at bay - the charge of the light cavalry into the flanks and rear of heavy mounted men is a significant threat they will be compelled to avoid. At that point, compelled to an act of impudence by the thought of their castle walls being undermined, the defenders will have committed a grave error and allowed your hero's men to prevail in a fair contest on open ground, where their mobility and superior ranged capability will allow them to cut the heavy horse to ribbons as they chase the kiting light cavalry all over the field.

4. The worse alternative for your hero would be that the defenders discover the sapping but are too cowardly (or clever) to rush to prevent it - or perhaps they are just too stupid to notice it at all. In this case, they wait inside and prepare for your hero's mined wall to collapse - they know he can't have begun more than one serious tunnel in the short time he has - and they will construct interior lines of defense, such as wooden stockades, to blunt your hero's attack when the wall comes down. At this point, your man must win his day in one of several riskier ways - he can indeed attempt a night attack where he doesn't pull the supports out from his tunnel and instead uses it to come up somewhere inside the castle grounds secretly, funneling men inside as quickly as possible to overwhelm the defenders with a secret strike. Alternatively, he can collapse the wall and make his charge, preferably with heavy use of his archers to rain fire arrows upon any breastworks or palisades constructed within prior to the assault - this will still be very hard, but not as hard as assaulting the castle intact. This really sucks for your hero, because he conquers the castle by rendering it LESS defensible - a quality of its construction he will desire a short time hence - but the necessity of war trumps the darling of perfection, I suppose.

Basically, your hero is going to HAVE to win this one by trickery instead of bravery, attrition, or overwhelming numbers. The context of the situation demands it.

Answer 4

Trying to take a castle 'in a few days' is a virtually impossible proposition. If the defenders know that a relief force is coming, there is virtually no reason outside of total stupidity to not simply wait within the castle for the reinforcements to arrive. A direct assault with ladders etc would be bloody enough to cause a defeat in the second battle, and the defenders will very reasonably expect a night attack and maintain alertness for this.

Here's an idea: Why not invert the problem? It seems like the real goal is to defeat the superior reinforcing army. There is no actual need to take the castle at this time. So a clever plan might be:

1. Make to attack. Naturally the defenders will retreat within the castle.

2. However, do not assault the castle! Instead, with the engineers, construct a strong barricade, dig pits and place traps to block the gate of the castle. Possibly do this at night, under cover of snow so this is hidden.

3. Now engage the relief force. The relief force will be expecting reinforcements from inside the castle... but it will never come. The cavalry inside the castle will never be able to get through the pits and barricades that were dug. With their plans thrown into disarray, the second enemy army will be easily defeated.

4. With no more hope of reinforcement, our hero can now go to the defenders of the castle and quite simply dictate terms of surrender.

In other words, use the enemy's quite reasonable caution against them. If you want your protagonist to look really clever, you could fabricate a 'desperate, failed assault' on the final day. Make the enemy think they've got the hero right where they want him - pincered between the heavy cavalry in his rear and enemy infantry coming up the slope, before revealing what was the real plan.

Answer 5

This is a straightforward military problem with several solutions.

1. Best solution: Avoid the battle.

Battles are fought for a reason. The gains your hero's army acquire from fighting a battle must outweigh the expenditure of resources (men, materiel) to achieve it.

Looking at a situation, I noticed 2 things: A. Its the climax of the story, which means that your hero's army has won other engagements in the past and have pushed the enemy to its final defensive position. B. The enemy is boxed in the valley.

There are plenty of reasons to force a battle (mostly for political reasons in cases like these), but the practical solution is for your hero's army to bypass the valley altogether and instead maneuver to control both entrances of the valley i.e denying the enemy's routes of resupply, reinforcement, and breakout.

The hero's army will then be free to operate in the enemy's rear areas: Seizing towns, supply depots, leadership, etc. This will make the enemy's position untenable, and you can force him to surrender, or to sally and leave their position to engage you on your terms, where you can destroy them by encirclement (with your superior numbers), or defeat them in detail (using maneuver to isolate smaller portions of his army and defeating them piecemeal).

2. Or you can destroy him with stand-off weapons.

This is where your army takes defensive positions and construct fortifications (say trenches) and have your engineers build artillery (ballistae, catapults, etc) using trees found in the area.

You can then pound them to submission.

3. The least desirable solution is to assault.

If for some reason you just have to fight him there, then you can assault him head on in a battle of attrition, hoping that your numerical superiority will carry the day.

A heavy cavalry is useful when they can charge. If they're bogged down, surrounded by trained infantry, they're done. Their armor isn't going to do much. So you advance, and you take their charge -a disciplined body of troops should be able to do this using formation- and prevent them from resetting the charge: you have your formations dense enough to stop them from charging through. Then you continue to advance until you close in with the enemy, robbing them of their space to maneuver and grind them to dust under the heels your uncountable legions.

Be advised that this battle will be costly, and you will lose a huge amount of resources in order to achieve an objective that you may be able to bypass. In essence you could win a pyrrhic victory.

If this is the case, then while your hero were able to win the day at the valley, he wouldn't have enough army to do anything else, leaving him vulnerable to treachery, enemy ally attacks, and unable to secure his gains effectively. This may be what you're going for in your story though. It could make a compelling drama.

Answer 6

I would suggest an Agincourtesque approach. Given, at Agincourt it was very muddy and the French were very Agincourt. However, the English were also greatly outnumbered. In this scenario you have more troops than the enemy and you're in a valley, not a forest. Here's what I'd suggest.

If you have access to the valley sides and if they are woody then send archers down the sides of the valley. If suitable you can send your light cavalry round the side but keep the flanking forces poor of sight.

Advance through the center of the valley slowly with people building palisades and ditches in front followed by heavy spear/pike infantry followed by a legion of archers.

When the enemy charge they would receive a lot of arrow fire on the way over, meet a palisade/ditch with spears/pikes, and maybe a slow ditch building peasant or two. When they actually started to make it past the palisades the light cavalry would charge down the hill. The already deadly flanking movement would be enhanced by the downhill charge. In short, your enemy are dead.

What if your flanking crew is noticed? That's what the archers up there are for. Shooting downhill is easy. While the enemy move up to take out your flanks your central army can also shot them in the back. And if they make it too far uphill your light cavalry can charge down.

The cavalry is dead.

Edit: If at all possible you should get your mountain archers to roll down stones, logs, etc...

Answer 7

Here are a few implications of the scenario you've described:

1) If the castle is at the head of the valley, then an assault on the castle starts with charging uphill. This is a bad thing.

2) If "The valley is quite cramped, and the hills are too tall and steep for any horses or heavily armoured men to climb without great difficulty", then it's likely that there is no agriculture in the valley. Which then implies a relatively barren, and probably rocky, valley floor. Thus, no "off-roading" for cavalry, leaving a prohibitively narrow field of battle.

3) If "The fight also takes place during the winter, adding shin-high snow as well as strong winds into the mix", then cavalry of all sorts will be disadvantaged. All cavalry is going to be moving slower than normal, especially off-road, which implies narrow or broken formations for cavalry.

4) Barring an existing weakness or point of ingress, "some engineers and sappers" aren't going to bring down a wall in the few days available to them.

The villain's pikemen and heavy cavalry can't work together in the narrow valley (unless maybe the pikemen are following to prevent the cavalry from being surrounded and cut off - oops, looks like the villain set a trap of his own). The hero's archers might be able to clear the walls for a frontal assault, but that means using the light cavalry as besieging infantry and, in any case, it doesn't sound like the hero has the overwhelming numbers that would be necessary to overwhelm the veterans manning the defense.

As described, the villain would have to be crazy to venture from the castle and the hero would have to be crazy to attempt an assault. The only way to defeat the villain in this scenario is through the traditional means of concluding a successful siege: subterfuge or treachery. That is,

1) Somewhere in the villain's forces is someone willing to open the gates for... reasons. 2) Somewhere in the hero's forces is someone willing to try to infiltrate the castle and open the gates.

Which means you've switched from the field of battle to politics or sabotage as the focus of your climax. Do you have lots of foreshadowing in place for that?

If you want a tactical battle as the climax of the novel, you probably need to move the castle to a position where the villain can be tempted to sally out in force. Maybe a broad valley full of worked land with the castle situated high on one side and the hero not sure where the reinforcements will appear?

Answer 8

Night time assault.

Usually works well with a protagonist or hero character that makes the call to do so. Night is messy...its dark, people are weary and tired, garrissons are limited. When you talk ugly mess of a battle, skill and troops equipment means less and morale/determination becomes a much stronger factor. Individual efforts can also shine through in this scenarios, gives a chance for a hero or two in your protagonists ranks to stand up and make a name for themselves if so desired.

Heavy cavalry becomes harder to us and can be caught dismounted in a surprise night time attack. Reversly, small amounts of light cavalry cam be quite sneaky in moving in.

Edit to add...the weather you have stated just adds to this night time confusion. Not only is it cold and dark, but a howling wind makes it that much more difficult to rally the defenders and turns the entire event into mass chaos. In this case, mass chaos is in your heros favor

Answer 9

Heavy cavalry's main weapon is momentum. No matter how heavily armed and armoured, they're almost useless when stationary. But they can't break a good schiltron or phalanx.

So form your pikemen into big hedgehog. Creep it forward, with archery support on the wings or behind, until they have to charge or be charged. Alternatively use your archers to shoot & scoot, running away behind your infantry if threatened.

Answer 10

I would suggest to invert the initial locations of the forces. If the defendants' heavy cavalry has easy access to the keep, they will likely go to it, or not leave it, unless they have a (quite harebrained) honour code that forbids them from refusing battle.

So I would suggest that they are a first stage of reinforcement, that - perhaps due to deficiencies in command or organisation - arrives earlier than the main reinforcing army. In that case they would be more motivated to attack, if they cannot circumvent the assailants' position.

Another option is to feign a retreat - better even a disorganised retreat - to goad the heavy cavalry into a persecution, and then surprise them at the other end of the valley. Better even if some engineers could then block the way back to the keep. But this must also rely on overconfidence, for they would normally send spies and scouts before engaging in a persecution.

Answer 11

Other answers mentioned this, so I won't go into too much detail on this point, but this battle may not need to be fought. If the valley is the only practical access point between these two countries, and the protagonist is fighting for independence, then holding this valley might be enough to force the enemy to negotiate terms. However, assuming that for political reasons the main enemy force needs to be defeated decisively, here we go...

This battle hinges on the protagonist being able to position his forces such that they are able to defeat the enemy reinforcements when they arrive. One position would be the castle (obviously). Another option would be to march past the castle, and position his troops at the opposite entrance to the valley. This would give them time to dig some fortifications and occupy the high ground (relative to the enemy reinforcements) while also constructing siege equipment.

A lot hinges on just what exactly defines the "heavy cavalry". Even in the late Middle Ages to Early Renaissance there was a wide variation in heavy cavalry, with the heaviest being eastern cataphracts employed by the Romans (Byzantines to us). Furthermore, it is not just the equipment of this cavalry that determines their combat value, but also their training and discipline.

Armored troops are generally fairly safe from archers, except at point blank range. Most arrows were not of high quality, and most archers were not particularly well trained (except for professional troops, such as the English yeomen archers of lore). A commander who anticipates making heavy use of his archers will invest in their training and attempt to purchase high quality arrows, but these are not always available or up to standards (a common complaint of English commanders during the Hundred Years War).

So while the archers may be able to injure the horses of the heavy cavalry, the men themselves (knights? or are they professional troops?) have little to fear from archery. While pikes traditionally are a good defense against cavalry, they are by no means foolproof. The Polish Hussars are a good example of heavy cavalry who excelled at breaking infantry formations in a head-on charge. This was due largely to their skill at maneuvering in tight formation and repeatedly charging.

The terrain of this valley may preclude such tactics, in which case the cavalry commander would likely remain in the castle. If he is unable to charge repeatedly to break the protagonist's infantry, he has no reason whatsoever to leave the castle. His troops are likely well armored and would serve equally well defending the walls as they would mounted on horseback. Unless he has made gross tactical errors, he likely had scouts watching the valley approach and will be aware of the protagonist's forces.

Logically, if he is a disciplined commander, he would dispatch messengers to the main army informing them of the situation and the composition of the protagonist's forces. Then they would wait for reinforcements, or to repel an attack on the castle. You need only look to the crusades for many instances of armored knights holding castles for long periods against larger armies for an idea of how this situation would play out. No such concepts as "honor" and "chivalry" would compel them to engage in a suicidal fight. Throw aside all that nonsense that Hollywood and Sir Walter Scott made up about "Lawful Stupid" knights. Medieval nobility and their men at arms were lifelong warriors, and while oaths of allegiance were very important, in no way did they interfere with commonsense tactics and strategies.

The only situation where the enemy cavalry commander would attack would be if he felt that his forces had a very good chance at routing the protagonist's army. However, if he lacks good knowledge of the protagonist's forces, then it is likely that the protagonist lacks good knowledge of his forces. I saw another answer indicating the 'lack of light cavalry' would make scouting difficult for the enemy commander. That's nonsense. He's in a valley, he has horses. He will watch the approach and have scouts make note of the protagonist's approach unless he is hilariously incompetent (which is always possible, if you want).

So, the way for the protagonist to defeat the main enemy body is through positioning. If he can cut off the castle, and isolate its defenders, he has a reasonable chance of holding the valley entrance against the approaching reinforcements. The castle itself is unlikely to do him very much good, since even if he took it that would just leave him vulnerable to a siege by a larger force free to cut him off from resupply.

By holding the valley entrance, the protagonist is able to maintain his lines of communication back home and also to prevent the enemy army from moving through the valley (where they could cut him off). His archers will benefit immensely from the high ground, and his light cavalry can easily maintain the siege of the castle while still being available to reinforce the main army if needed desperately.

The resolution to this situation would come either when the enemy chooses to assault his position (fortified with the benefit of several days, and uphill at that) or if the enemy declines battle, the castle would eventually have to yield. Given the winter weather, the enemy force would need dramatic materiel superiority to succeed in an uphill assault against a fortified position. If the enemy force truly is strong enough to dislodge the protagonist from that position, then they should probably withdraw and fight a guerrilla campaign.

As I see it, holding the valley entrance is the strongest position for the protagonist to take, and it expends the least amount of effort/casualties to occupy. There is a slight risk that while they are bypassing the castle the cavalry may sally forth to attack, but this risk exists no matter what course of action the protagonist takes.

Hope that this analysis helps, and be sure to consider the training/experience of the troops with different scenarios (the sappers would surely be helpful in preparing fortifications for the protagonist, for example).

Answer 12

The enemy is lacking in light cavalry to use as a scout force, so how does he (or she) know what your hero is doing? Presumably they are working mostly on rumour and guesswork.

They also have duty and obligations that go with the castle they command. It sounds like the castle controls an important trade route, so keeping the trade route safe is likely part of their duties.

Now imagine they receive a letter saying that several trading caravans are stuck at a nearby town, unable to venture forth because of the rebel army. Cold, disease, and starvation, so the letter claims, have reduced the rebel army to nothing more than a few bands of thieves. They demand that the commander stop hiding like a coward, and honour his treaty obligations to ride forth and escort their caravans past these starving thieves and brigands.

Now duty and honour compel the commander to come out from his (or her) fortress. Their arrogance could easily make them think that riding out in full ceremonial dress and leaving the scruffy infantry behind is the right thing to do.

The next step is to break their morale. The conditions you describe are terrible for cavalry. Horses have very fragile legs, and a broken leg is a death sentence for a horse. Trained race horses will sometimes refuse jumps if they can't see the other side, even in the olympics. It comes down to the horse trusting that its rider is leading them somewhere safe. Break that trust. Dig holes in the road and cover them snow. All you need to do is get the horse worried about its footing. Keep it subtle. It's ok that they suspect they are riding into a trap, which they probably do, but it can't be so overt that honour and duty stop compelling them to advance.

Now let them see your hero's infantry. Disciplined infantry vs cavalry is often a stalemate. The infantry cannot catch the cavalry. The cavalry cannot breach the infantry's turtle defence. But this cavalry has horses that won't charge over snow. They can either retreat, and be called cowards and break their treaty obligations with those merchants, or dismount and fight on foot.

The battle is now between a discipline trained infantry on a morale high, and heavily armoured cavalry improvising at being infantry. Their armour slows them down and they lack the training to fight effectively as a foot unit, but politically they can't refuse battle.

Whilst the cavalry is out of the castle fighting the infantry, is the perfect time to try and take the castle. The plan may not work after all. They simply walk in disguised as humble fire wood merchants (it is winter after all, the castle must need fire wood), reveal their weapons and announce they are now in charge. The leadership of the castle is all out on the road defending their honour, so who is going to say no? If someone does say no, then it needs to be nipped in the bud with maximum aggression. A horn is sounded to tell the rest of the army to double time it up the road. Provided the gate is kept open long enough for them to get inside, you win.

If it doesn't go well, set fire to all the firewood you just brought in and hope the castle burns to the ground.

Answer 13

Assuming the following:

Enemy reinforcements

Castle-> it's silly to put a castle in a narrow valley; you want to put it at the end of the valley to maximise the bottleneck, and prevent some enterprising Hannibal from getting siege weapons on higher ground

Valley full of enemy troops

Hero+ army

in that order, the strategy looks simple:

Take your least experienced infantry and archers and have them and your sappers scale the mountains on both sides and work their way along until they are just past the enemy stronghold in the valley, but well before they reach the castle. The sappers then set explosives at that point back towards your camp. Black powder was available (if rare) in the late Medieval period and will suffice.

In the meantime, your heavy infantry set up a wall of pikes to withstand a cavalry charge in front of your camp. This can simply be sharpened saplings buried in the ground. Once the sappers are ready, set off the charges and bring the mountains down over the enemy camp.

Since they can't retreat towards the castle, they will have to charge out of the valley in order to survive, right into your pikewall.