Thursday, November 26, 2009

The official soundtrack to this blog.

I recently stumbled upon this band on youtube and have to support anyone who sings about Sparta.

Monday, August 31, 2009

Crowd density

I am often asked how and why men enter the close-packed formation needed to conduct the othsimos as I define it. Here is a little video by some reenactors showing how to breach a shield wall. Note the lengths they go to to keep their men packed belly to back. If Hoplites conducted short terminal charges directly into othismos- as opposed to long running charges straight into othismos, which I doubt- then this is how the men packed. Only by packing tight can you transfer your aggregate force. These guys in fact charge too far, since any distance past that needed to achieve their "ramming" speed is wasted. Because close order is more important than velocity, this can be done from very close range after a period of spear fencing as well as from the opeing of combat.

The only way to resist men in this formation is to match it. A dense, close-packed phalanx will simply absorb this. Multiply this interaction along the front of a unit within the phalanx and you can see how it occurred.

Tuesday, July 14, 2009

The Harmodios blow

I recently re-read a paper on Greek swordsmanship:

“Footwork in Ancient Greek Swordsmanship”
Brian F. Cook, Metropolitan Museum Journal, Vol. 24 (1989), pp. 57-64

In this paper an overhead strike is discussed. With minor variations it appears as below.

From the paper:

“The so-called "Harmodios blow" studied by Shefton, who coined the useful term by which it is now fairly generally known. This is a slashing movement named for the action of Harmodios in the marble statuary group of the Tyrant-slayers best known from a Roman copy in Naples. The moment most frequently represented is the point of stillness when the sword- hand has been raised head-high with the sword pointing backward over the shoulder in readiness for a downward slash. The blow may be delivered either forehand (Figure 1) or backhand (Figure 2). Philip Lancaster, of the Department of Edged Weapons at the Tower of London, who kindly gave advice on some practical aspects of swordsmanship, pointed out that this movement would be hazardous under normal combat conditions: not only is there some danger that it would put a swordsman off balance, but the action would also leave the sword-arm unprotected and vulnerable. B. B. Shefton had already noted that the sword when raised could not be used for parrying, and that in close combat the blow therefore required careful timing. It would have been particularly dangerous for a Greek hoplite in leaving the armpit exposed above the edge of the cuirass.' A further disadvantage of the Harmodios blow is that it was less effective than a thrust against a well-equipped opponent: it would probably have been resisted even by a padded linen corselet, which would have been vulnerable to a thrust, and would certainly have been ineffective against a metal cuirass." In combat, then, the Harmodios blow can only have been a desperate measure, employed when the vulnerability it imposed was outweighed by a greater danger.”

“Finding no examples of the use of the Harmodios blow before the closing years of the sixth century B.C.,' Shefton connected it with the introduction of the spatulate sword, a more versatile weapon than the straight-edged sword, which is most effective in an underhand stabbing or thrusting movement. It is around the same time that warriors began to be represented in Attic red-figure in a stance that, al- though it soon became conventional, may reflect the kind of simple drill-movement for which no literary evidence survives. The movement is in fact so simple that no specific comment was made by ancient authors: like so many minor details of life, it was too familiar at the time to call for explanation.”

Now the above may all be true, but the Harmodios may not have been so dangerous and unlikely as thought by the authors above. In fact the Harmodios blow might be one of the few strikes available to men who are standing in synaspismos, close order with overlapping shields. If men are in close as I have described previously, shield to shield, then the right arm needs to not only strike in this fashion, but also move in this way to ward the head. I have been experimenting with how one could fight in so close, with only the raised right arm given freedom of movement. The answer is very much like the harmodios blow. Better yet would be to adopt a shorter blade like the Spartans may have done.

An interesting note on swords is that the sword (xiphos) is slung in a sheath high under the left arm, almost like a shoulder-holster for a pistol. I have been told by hoplite reenactors that this makes drawing the sword much easier in the confined space of a fighting phalanx. The manner of hanging the sheath may thus be yet another feature of the panoply designed for fighting in crowded conditions.

Tuesday, June 23, 2009

More on crowd pressures

Here is some information from a paper on the pressures generated by crowds:

"Prediction of human crowd pressures"
Accident Analysis and Prevention 38 (2006) 712–722
Ris S.C. Lee, Roger L. Hughes

In situations where pedestrians are crushed, the density of the crowd is extremely high and the physical movement of pedestrians is almost impossible. When crushing occurs, the high pressures developed within the crowd, which can bend steel barriers or push down brick walls, can be unbearable to some members of the crowd, producing fatalities from asphyxiation while still standing. Generally, the highest pressures are felt by those pedestrians near any barrier that is checking the advance of the crowd. Such pressures will gradually restrict these people from breathing. Each time a breath is exhaled the weight of the load restricts inhalation of the next breath. A slow death caused by suffocation usually follows, unless rescue is immediate. The internal pressure in a crowd on the time scale of a minute or so is thus the critical criterion for determining the likelihood of an accident involving crushing in the crowd. Tests on live subjects conducted by Evans and Hayden (1971) found that the tolerable force was typically 623N for men when pushed against a 100mm wide flat bar. This force increased to typically 800N when the subject was allowed to push against the bar to reduce loading on his rib cage. For women, Evans and Hayden (1971) reported the tolerance levelwas significantly less. Apart from Evans and Hayden (1971), studies on exploring the magnitude of loadings that could cause crush asphyxia found that death was estimated to have occurred 15 seconds after a load of 6227 N and 4–6 min after 1112 N was applied, see Hopkins et al. (1993). It should be noted that loadings of such as these magnitudes are affected by various factors including age, gender and anatomical build.

From the paper we can see the crushing force generated by the crowd at a rock concert over time (the lighter plot is a prediction, ignore it).

The amount of pressure that is fatal to a human varies depending on the duration, since the asphyxiation can occur over time as described above. Very high pressure (6000+ N) can be almost immediately lethal. From the plot above we can see that over the time period of recording from 5-10 minutes, the crowd pressure was almost never below 800N and reached a peak of 1,500N. Since 623-800N were described as a tolerable limit above, and pressures of 1112N lethal, this crowd would have been intolerable and potentially lethal for most of the period. In the concert many people had to be passed out of the crowd and treated by medical professionals.

From another paper:

“Experiments to investigate the level of ‘comfortable’
loads for people against crush barriers”
R.A. Smith*, L.B. Lim
Safety Science 18 (1995) 329-335

The same authors measured loads at several ‘pop concerts’, where at one they measured
instantaneous peak values of up to 4.2 kN/m, 30-second average values up to 1.8 kN/m
and sustained loadings of typically 1.5 kN/m lasting for 10 minutes. Throughout the first half of an act the sustained average load was 0.8 to 1 kN/m. During the concert, people pressed against the barriers and in distress were rescued by being pulled over the barriers and being treated by medical staff.

This paper had an interesting figure that showed how the pushing force could vary with the degree to which men leaned forward against the man ahead. How this would correlate with forces that hoplite would generate is not really known, but the important thing is to note that the behavior of the men in the crowd can alter the amount of pressure generated. As few as 4-8 men are producing lethal pressures (note the scale of the y-axis is Kilonewtons (1,000N). This data is not even from an especially dense crowd, they can be almost double that density and proportionally more deadly.

The importance of this graph is that it shows that through behavior the amount of force generated by a crowd can be increased. Here simply leaning forward more transmits more force forward. The implication is that through training men can transfer greater force forward more efficiently. This, and other behaviors, is how the system can be tweeked to produce more with training.

Modeling hoplite combat

I have, after years of trying off and on, finally gotten in contact with Rob McDermott. If you have not seen his simulation of hoplite combat take a look:

There are many elements that could be added to raise the realism of the model, but the most important thing is to show how a group behavior, such as phalanx combat, can be self-organized. In this model there is no leader. Each simulated hoplite is an "agent" endowed with a list of very simple responses. The only information they recieve is from their immediate surroundings- from the few men around them acting to push or fight them. One of the biggest problems that those who follow my blog have with my view of phalanx combat is that they don't see how such crowd-wide behavior could be coordinated. Rob's model gives an example, though I would change/add a variety of the details I've exposed in previous posts. I plan to create a model with those elements in the future.

Thursday, January 22, 2009

Crowds don't need to be big to generate extreme forces.

One of the most common objections to my model of the othismos phase of hoplite combat as essentially two crowds moving against each other stems from the fact that for most readers the mechanics of crowd pushing is counter-intuitive. They simply do not believe that "crowds" of only a few ranks deep can generate lethal force. To make this clearer I'm posting some snippets from J. Fruin's "The causes and prevention of crowd disasters."

Crowd forces can reach levels that almost impossible to resist or control. Virtually all crowd deaths are due to compressive asphyxia and not the "trampling" reported by the news media. Evidence of bent steel railings after several fatal crowd incidents show that forces of more than 4500 N (1,000 lbs.) occurred. Forces are due to pushing, and the domino effect of people leaning against each other.

So our common notion of "pushing" may not be adequate to completely describe what occurs. The most force may actually be transferred through coordinated "leaning" when crowd densities are very high.

Experiments to determine concentrated forces on guardrails due to leaning and pushing have shown that force of 30% to 75% of participant weight can occur. In a US National Bureau of Standards study of guardrails, three persons exerted a leaning force of 792 N (178 lbs.) and 609 N (137 lbs.) pushing. [9] In a similar Australian Building Technology Centre study, three persons in a combined leaning an pushing posture developed a force of 1370 N (306 lbs.). [10] This study showed that under a simulated "panic", 5 persons were capable of developing a force of 3430 N (766 lbs.).

Only three people exerted a force horizontally against a target by simply leaning into each other that would be the equivalent of the weight of a grown man laying on top of you. Now, you may think that you could bear this weight without suffering from asphyxia, but for how long? If the pressure from even this small group were maintained for any length of time you would succumb to exhaustion and be unable to inflate your lungs. The effect is similar to what occurs when constricting snakes, like pythons and boas, kill. The don't so much crush the breath out of you as simply make it incrementally more difficult for you to expand your diaphragm to take in air.

Another common assumption is that two opposing groups could not generate these forces against each other, that a crowd must be pushing in one direction against a wall. This next quote shows how crowd collisions can be deadly.

In the Cincinnati rock concert incident, a line of bodies was found approximately 9 m (30 ft) from a wall near the entrance. This indicates that crowd pressures probably came from both directions as rear ranks pressed forward and front ranks pushed off the wall.

I hope this demonstrates that phalanxes of 8 ranks could be deadly. Simply scaling up the leaning force from 3 people (178 lbs)to 8 people gives us 475 lbs. There is surely a loss due to lack of coordination, so this figure is probably high, but it shows the principle.

Taking just the conservative leaning estimate, 12 on 12 would be over 720lbs and 16 on 16 ranks might approach 1,000lbs.

Now how exactly to scale up these pressures I do not know, so these are simply ballpark figures. Perhaps they reflect peak pressures, or peak pressures might be much higher. Sustained pressures are smaller, but even a fraction of this force would be deadly unless the hoplites were protected by the aspis. Peak pressures could surely even crush the aspis, as we know occurred in some battles, which would then leave the hoplite defenseless against further compression.

For some further reading: