How can you stop a triceratops charge?

You have just received info that the main force was completely routed by an enemy army with triceratops cavalry. Their pikes and arquebuses did not have the stopping power to halt the armored triceratops, so they were scattered and defeated. However, they seem to have worse weaponry and tactics than your forces, so you might be able to win if you can stop the cavalry charge. How can you do this?

You have 2 tercios of 2500 reasonably well-trained men each. Each tercio is divided into 10 companies of 250 men, with 6 companies of pikemen and 4 companies of arquebusiers. You also have 5 field cannons. It can be assumed that the enemy will have higher morale than you troops, since they have just achieved a victory. You also have a camp fortified with a palisade.

The enemy is arriving in 6 hours. According to your scouts, they have a formation of 50 armored triceratops one rank deep, with 2 knights mounted on each. They are supported by some 4000 medieval infantry, armed with spears and swords, and 1000 trained archers. The battle takes place in a mountain pass about 100 meters wide, so they will not be able to flank you. However, you cannot afford to retreat, as this will result in great loss of territory. You can assume that the enemy will not be fresh, as they have been marching for a long time. You can also assume that they will attack with a cavalry charge.

Assuming sufficient supplies for both forces, how can you halt the killer cavalry charge?

Ditch traps, boulders rolling down from the sides, big caltrops, fire traps or fire arrows. Cavalry is weak against prepared positions.

If you know what they have and where they're coming through, and you have a workforce of thousands you can just prepare traps and caltrops for them. Either enrage or confuse the beasts or kill/maim them outright. The triceratops will be a danger and obstacle to their own infantry.

Now we can add an exhaustive list where we add everything from 50m high walls to stakes and caltrops. My answer tries to give the most economical practice to stop this charge. A minimum to stop them. We only have 6h anyway.

The terrain can make a lot difficult. In war ditches are the best defence. Easy to construct if the ground is good, little logistics and effective. Compared to a wall, the enemy first needs to go down a slope, slowing them down or risking falling and injury. Especially with an armoured triceratops. Then they need to go up. Especially in a charge this is tiring. Ever tried to run up a hill? It is slow and not very good. Now add in all the other defences. Caltrops first. They are incredibly effective and cruel. A low (or if you have time, high and wide) wall, stakes, spears, a rain or arrows. All now viable because the charge isn't a charge any more. It is a careful drop down and a difficult move up a slope.

However, as you're in a pass digging might not always be feasible. You might need picks, the environment can become unstable, it takes time and a whole range of other small problems. Digging a ditch or several in 6 hours can also be difficult and tiring of your men. That is why you can use a tactic they used against elephants. Pigs.

The accounts differ, where pigs were set alight, were injured or just let loose against elephants. Whatever you do, the chaos of battle will cause the pigs to squeal. These creatures squeal loudly. The elephants became scared of this, and if one routed more follow. They would injure themselves, their riders and anyone in their way, which was most likely their allies as they ran in that direction.

Now put this to triceratops. Granted, I'm making a leap that their peanut brains handle the same as elephants. I would argue they would actually be worse than elephants because of it. As herd animals they are more likely to run from predators for safety. Their peanut brain isn't as easily trained for combat as a horse or elephant.

We couldn't dig a ditch in the pass. The triceratops arrive 50 abrest and charge. Suddenly a hellish screaming of burning pigs comes at them. The screams and fire working on their brains, overruling any training they had. They only know one thing. Run away. They try to turn, not thinking about their neighbours. They injure each other, the screams of triceratops adding to the chaos of milling bodies. They run back towards their allies, not stopping as they go straight through their lines, though they likely try to avoid any platoon if they can to run away more freely.

The all the defenders have lost are a few of their pigs, and hunger in their ranks as they smell the air rank with burning bacon. A small price to pay for standing in front of a 50 armoured triceratops charge and coming out unscathed. The first battle won miraculously, their morale so high while the enemy has just seen their awesome weapons defeated in a single swoop.

Many triceratops are injured and can't fight, causing a huge drain of resources to care for them. Many might be killed as a tactical decision because of it. Others need to be captured again. They might still fight in the war, but they'll be much more careful when they are used. The enemy did seem to have an awful lot of pig farmers. Which is why they started the war in the first place.

Given that your army is well supplied, it may perhaps have a stock of rattlesnakes on hand for military maneuvers, food, and making a salutary example of a deserter or two. Otherwise most of your men will have to spend some time on those hills overlooking the pass with pole and looped cord.

There's a story that even European horses freshly brought to the New World were frightened by snake rattles. Whether or not that is true, the sound would certainly affect the riders, and the beasts might respond to their fright. While a Triceratops seems too large to care about venom, we should bear in mind that rattlesnake venom has a localized necrotic effect that could lead to a life-threatening infection, so wild Triceratops would have reason to become naturally selected to give them wide berth, if they coexisted for some span of time.

Assuming the Triceratops charge came first, and the army had time to prepare other previously ineffectual measures like spears, there would be plenty of terrain to hide the snakes until the last moment. Success of the measure would depend on large part how careful the animals' feet were armored. I assume they would have more than horseshoes to protect them from caltrops, but I doubt they are entirely surrounded in metal. If some were bitten right away, they might communicate this fact to the others and cause a general "loss of morale" for beasts and men alike.

Most Non-gun troops: Build an obstacle course / killing field across the entire 100m approach from just beyond the palisade to 100m away. Build ditches, pits and banks. Cut down trees and large branches and unevenly pile them up in unstable heaps propped against one another amidst the earth works and add piles of stone. Then scatter caltrops and embedded spikes into the whole area. Build the strongest / highest obstacles to either side to force any charge down the centre to cause congestion.

The remainder of non-gun troops: Reinforce the palisade with logs and ensure that there are well protected firing holes for 100 arquebusier and all 5 cannons.

All gun troops: Arrange the cannon and arquebusier companies across the palisade in the prepared positions and ensure they are as well protected as possible by the palisades / wood and shields. Gunners should be instructed to fire at any massed enemy entering the killing field especially cavalry. Cannon fire should be concentrated on any Triceratops.

The gunners should practice maneuvering behind the palisade ahead of time in “lanes” to ensure that they can rapidly and efficiently fire and move to the rear to reload then queue to fire again in an orderly fashion. With 8 companies of perhaps 100 per company and a 100m frontage 100 weapons should be available to fire at any one time. Ensure that sufficient supplies of ammunition are properly distributed.

If there is time some consideration could be given to providing additional cover from indirect arrow fire with angled palisades and shields at key points such as reloading areas and immediately behind the main palisade.

The result Any charge into such a position would be catastrophic as the troops would be forced into an impossibly narrow frontage where they would be gunned down in heaps. It would be impossible to form any organized body of troops with any momentum. As the casualties mounted the obstacle field would merely grow in size and change in composition.

They have forward momentum, which you want to turn into upward, self-impaling and wrecking momentum. Which is how most pikes against cavalry actually work. The mount drives into it, the forward impaling momentum turns into im sliding up the pole i impaled myself momentum, resulting in further impaling when you slide back down dragged by gravity.

So a triceratops weighs roughly 6 to 12 tons. So its shopping time for anti-tank, anti-vehicle stopping pillars. The problem is, we do not have time for proper foundations. They need to deploy on the fly and they need to be held in place- by the tricoperators itself ideally. So the thing keeping it upright, is not a man, but the mount putting weight on some plate. Once the spear is lodged in place, the trap can tumble and fall over. It has done its job.

Or its job is just starting, the obstacle itself, is just the lever and the plate is the spear driving into the mount.

Flanking fire from the hills

So - given the Six hour time frame, digging a sufficient Trench is possible, but going to be difficult.

Assuming further that the Triceratops charge with their heads in a downward position, negating the effectiveness of pikes.

However - the Human riders, even if they are in medieval style plate armour - are going to be vulnerable to fire from an elevated position by the arquebusiers. You have approx 2,000 of these - and their primary focus is going to be on taking out the 100 Knights on the fifty Triceratops.

100 metres is within the effective range of your Firearms - and by scaling the sides of the mountain pass - only a short distance (say fity metres vertically up) - you are largely out of the lethal range of Arrows and firing down onto your target, you have an advantage of being able to better target the rider, but also - any missed shots are more likely to hit the fleshy part of the Triceratops and do damage.

The Pikemen will be split into 3 sections - one manning the fortifications, the others on the side of the mountain pass, hidden.

The cannons will be arranged along the fortification walls.

The battle plan will be as follows:

They will have the instructions to aim specifically at the Knights on the Triceratops only, as they pass into their effective range. Each group of 10 arquebusiers will aim at a single Triceratops rider that is closest to them. Each group will likely get 2 maybe 3 shots off - so 20 to 30 rounds find at each knight, Per 10 man squad, every 10 metres. Once the Triceratops have past the effective range (and they would use the six hours to mark out engagement distances) - they would then focus the Archers.

Once all the Knights have been dispatched (which given the volume of Fire, I think is reasonable) - the Cannons will open up.

The goal here is more Shock and Awe and to get the Triceratops to reverse course and charge at their own lines.

Then the Pikemen on the valley sides charge down.

This results in 2 possibilities:

Option 1 - the Triceratops break their charge, turn back in the face of the cannons and charge through their own lines

In this scenario, the Pikemen wait for the Triceratorps to exit the engagement distance, then charge in with their pikes to mop up the survivors.

Option 2 - the Triceratops hold or dont counter-charge their own lines

In this scenario, whilst it is less idea as the Enemy formations will not be as disrupted, the charge down from the side of the valley with a pike, should allow the pikemen to inflict fatal injuries on the Triceratops into their flanks, as well as causing the foot soldiers to rout as they are caught in a pincer-like move, between 2 sets of charging pikemen.