What happened when Cavalry charged Cavalry?

[Patrick Waterson]

This has implications concerning whether a mutual full-on charge would result in shattered or merely rebuffed horses.

There are numerous images of horse v. horse collisions at speed on you tube.  They are not nice, as horses end up crippled or dead in several.  There is one good one in which two American quarter horses collide shoulder to shoulder at speed.  One horse and rider are sent sprawling.  The other horse stays on its feet but the rider goes over its neck.  Thankfully, both horses and riders survive this one.  So, from this small sample, we can probably say "shattering" isn't inevitable but it certainly happens.  This is also what you'd expect from any exposure to horse racing - not all falls and collisions result in death or serious injury but a proportion do.  The shoulder-to-shoulder collision is interesting in that you might expect a horse to avoid a head-to-head impact by angling its neck, with the impact being on the neck and shoulder, as in this case.

This is very useful; one obvious question would be the actual speed at which injuries start to result and particularly when they start to become the norm rather than the exception.  Cavalry charges in our period were not, as I understand it, conducted at racecourse speeds.

The effects of the collision on horse and rider are also worthy of note: they go down together or the horse stays up and the rider separates (he evidently was not using a Roman saddle!).

As to actual jousting practice, I've not read the many detailed accounts that exist to check them for collisions.  I would note though that the barrier or list between the two riders was introduced to reduce collisions and injuries to (very expensive) horses in the 15th century.

A valid consideration, albeit one might also observe that it was not introduced until the 15th century, by which time the weights of both horses and armour had increased beyond what had been available throughout previous history.  Whether this lack of barrier introduction was because injuries were rarer or horses less precious is of course another question.

[Erpingham]

Whether this lack of barrier introduction was because injuries were rarer or horses less precious is of course another question.

It is usually assumed to be due to a change in jousting fashion.  One-on-one encounters on a narrow course were originally rarer than team melees in a wider arena.  As the one-to-one high speed encounters became more popular, serious collisions became more common so safety features were introduced.

[Patrick Waterson]

I have had a look through various videos of equine head-on collisions.  One, in a 'sulky' (harness cart) race, had one horse plus 'sulky' going the wrong way around the track at speed while the rest of the field were going the correct way, at speed, and the resultant impact was lethal for both horses, although it was not clear whether death occured on impact or simply resulted from it (i.e. the animals being put down owing to broken bones or whatever).  Another, at a riding-in-mutually-interpenetrating-cricles rehearsal, conducted at the trot, saw both inexpert riders dumped on the ground but the horses were none the worse for wear.

Whether this lack of barrier introduction was because injuries were rarer or horses less precious is of course another question.

It is usually assumed to be due to a change in jousting fashion.  One-on-one encounters on a narrow course were originally rarer than team melees in a wider arena.  As the one-to-one high speed encounters became more popular, serious collisions became more common so safety features were introduced.

That makes sense.

We may be closing in on a weight-and-speed combination above which direct contact at speed becomes potentially injurious to mount and conceivably man.  This speed would appear to be above a mutual trot and at or below a mutual gallop.  Historical charge speeds seem to have centred upon the canter, with exceptions (e.g. at Issus, Alexander went to the gallop to avoid Persian archery - the Impetus shooting evade in reverse!).  My instinct would be that cavalry quickly developed a 'feel' for the kind of speed which would provide impact without sustaining incapacitating injury, and that this speed would also be commensurate with control and cohesion.

There is a further consideration: in war, losses which would be unacceptable on the training field would be accepted if it was felt they provided a battle-winning edge.  Hence even if a number of injuries resulted from 'rough horseplay' these might be considered acceptable if they led to success.  This would allow us to raise our 'impact index' into the realm of risk of injury.

[PMBardunias]

So what is the outcome?  Well, Justin calculated that the infantryman needed to experience a force of at least 307.8 N to be bowled over by the horse.  From the table it can be seen that the horse will knock over the first 5 infantry, but can probably be stopped by the sixth.  Any volunteers for the first 5 ranks?

I do not believe this is accurate. The horses do not collide as a solid mass.  If we assume that the infantry are in close order, essentially belly to back, by your calculations the horses would be stopped and the last 5 ranks knocked down like a Newton's cradle. But this does not happen, because the first horse hits the line of men and is stopped, then the second horse his the first horse and the line of men, third horse hits the first and second horse and the first horse and the line of men, etc.

We saw something similar when doing othismos experiments. Unless the hoplites are linked as one mass, the men ahead absorb much of the force from those behind. Arrian, by the way, tells us that horses cannot push in a linked manner as crowded men can.

[Nick Harbud]

Interesting....

The main purpose of my post was to point out that any calculations should be based upon conservation of momentum rather than conservation of kinetic energy, and that this would lead one to the conclusion that the effect of charging horses on a body of infantry would be somewhat less than calculated by Justin. 

Various videos that have been referenced seem to show that rather more momentum is transferred in the collision than I assumed and your practical experiments (with men) indicate that even this approach is somewhat optimistic from the viewpoint of the chargers.  In other words, instead of a charging horse ploughing through 7 ranks (as calculated by Justin) or 4 ranks (as calculated by me) it is probably a lower number, even assuming the horse is not put off by a solid line of infantry waving pointy sticks in its direction.

Incidentally, I accept no argument from ancient writers on the Laws of Motion.  Sir Isaac Newton tells us it is this way, and simply because one can demonstrate it in a classroom does not make it any less valid.   

[PMBardunias]

Interesting....

The main purpose of my post was to point out that any calculations should be based upon conservation of momentum rather than conservation of kinetic energy, and that this would lead one to the conclusion that the effect of charging horses on a body of infantry would be somewhat less than calculated by Justin. 

Various videos that have been referenced seem to show that rather more momentum is transferred in the collision than I assumed and your practical experiments (with men) indicate that even this approach is somewhat optimistic from the viewpoint of the chargers.  In other words, instead of a charging horse ploughing through 7 ranks (as calculated by Justin) or 4 ranks (as calculated by me) it is probably a lower number, even assuming the horse is not put off by a solid line of infantry waving pointy sticks in its direction.

Incidentally, I accept no argument from ancient writers on the Laws of Motion.  Sir Isaac Newton tells us it is this way, and simply because one can demonstrate it in a classroom does not make it any less valid.   

Think of it as the difference between getting hit by a train car or getting hit by a few cars in line of the same mass.  Any space between them means that the opposing force, the men in our case, gets to act on them one at a time. (How much they decelerate each in turn before the next one hits is something that we would need to test, but a line like a hoplites would stop each horse dead almost instantly.  Here is a real example of something heavy, me, hitting a line of men.  I weigh about 300lbs, and I ran and jumped into a line of men three deep.  Smaller guys, lets say 160-170lbs and stationary.  I bounced off and they did not recoil.  Against one man, or even two they tend to recoil or fall. If a line of "me" hit in succession, they three man line would just absorb the strike.  Moreso because it is now a 4 man line with the first me having to be accelerated by the second me before effecting the line because I am not effectively part of the mass of the line:)

[Patrick Waterson]

Just out of interest, here is a clip of a horse running into a car.  'Runaway horse gallops head-on into a BMW'  (There may be a 20-30 second ad before the clip begins.)

Did anyone expect the actual result?

[Erpingham]

Just out of interest, here is a clip of a horse running into a car.  'Runaway horse gallops head-on into a BMW'  (There may be a 20-30 second ad before the clip begins.)

Did anyone expect the actual result?

That's one lucky horse.  Usually what happens is far worse.  I wouldn't recommend this for animal lovers but the are many examples here.

[Patrick Waterson]

Yes.  I think 'head on' in the headline was a little misleading: from what I saw the horse impacted at an angle and rolled onto the bonnet.  It does at least show how a difference in the angle of collision (i.e. not being directly head-on) can make a big difference to the result.