Why would non-flanked formations rout?

[Erpingham]

true. Not enough space and file leaders being pushed back violently could start a ripple effect. Too much room and it could allow gaps to be generated and exploited.

Thank goodness nobody proposed a style of combat where you rammed into the back of the file leader, turning him into a human battering ram 

[Justin Swanton]

Deprive a man of that space and he is at a critical disadvantage - his opponent can avoid his blows but he can't avoid his opponent's. This suggests that a file is meant to fall back if the file leader needs sparring room. Question is whether too much falling back would necessarily precipitate a rout and - barring unpleasant surprises like getting flanked - it is the only thing that would precipitate a rout?

true. Not enough space and file leaders being pushed back violently could start a ripple effect. Too much room and it could allow gaps to be generated and exploited.

I'm thinking this is why surrounded troops were invariably slaughtered. They are in an unexpected situation and hence demoralised. This makes them more cautious in combat and they tend to give way, but being surrounded means the troops are soon jammed together and the front rankers can no longer fall back. Unable to recoil, they are at a critical disadvantage and are soon dispatched.

[Justin Swanton]

On the subject of backing up, I've notice that in every single form of combat that involves hand-held weapons one absolutely needs space to fall back in at some point in order to avoid the opponent's blows.

None of those examples involves a shield. Does having a wall of big shields to block your opponent's blows make a major difference? Is a spear-fighting hoplite expected to fall back?

The shield doesn't protect your face or legs. See here and here.

[Erpingham]

None of those examples involves a shield. Does having a wall of big shields to block your opponent's blows make a major difference? Is a spear-fighting hoplite expected to fall back?

Did some troops expect to fall back?  Probably.  Being pushed back a distance while absorbing impact may have been common.  Only if you you were pushed back too far or didn't seem to be able to stop might panic set in.

A general point on individual combat skills is that they may not replicate group combat skills.  For example, individual styles in medieval fight manuals allow for a lot of movement but how much that could be replicated fighting shoulder-to-shoulder in formation is debateable.

[aligern]

Surrounded troops need not be slaughtered if they are prepared for that event and form square or globus to deal with it. What kills people is the disruption of the fighting team which gives the enemy an advantage and the disrupted a disadvantage. Being disordered does for you because one of the disordered is fighting two three opponents.
Several of the contributions here make the assumption that files fight one on one. This is just not so. each man has the support of those to right and left and behind. Files cannot retire singly, they must together, as Duncan pointed out, the shield wall is important because shields do not protect one man only.
Roy

[Imperial Dave]

Assuming we have shieldwall formations of close packed infantry rather than looser troops with more emphasis on individual fighting styles

[aligern]

Even thise with looser fighting stykes have to depend on thise either side of and behind them when in close combat. In a loose formation withdrawal by obe file is still very difficult. I suspect that the Hollywood mixed melee woukd be abhoeprrent to either side in combat. Who wants their back ir head exposed to an opponent.

[Imperial Dave]

oh gawd, not the Hollywood mixed melee 

agreed that cover from ones neighbours in the line and behind is important. I wonder how more tribal formations managed files and 'cover' on multiple lines (as an aside)

[Jim Webster]

On the subject of backing up, I've notice that in every single form of combat that involves hand-held weapons one absolutely needs space to fall back in at some point in order to avoid the opponent's blows.

None of those examples involves a shield. Does having a wall of big shields to block your opponent's blows make a major difference? Is a spear-fighting hoplite expected to fall back?

we know that among hoplites there was a big thing about NOT falling back

But we read of other peoples who 'think it's no shame to run away' and would just fight for a while, then decide, 'Sod this for a game of soldiers' and just run away and hide and get on with real life

Remember a lot of ancient soldiers weren't soldiers, they were just men who were effectively fulfilling the equivalent of a tax obligation. When it came to motivation, they had no real expectation that the world after they won the battle would be particularly better for them and their families than the world if they lost a battle. (Provided they personally lived through the experience.)

[Patrick Waterson]

The battle of Delium (Thucydides IV.96) is an interesting case.  The Boeotians and Athenians have about the same number of hoplites.  The Thebans form up 25 deep on their army's right, leaving their fellow Boeotians to be outflanked.

The Boeotian left, as far as the centre, was worsted by the Athenians. The Thespians in that part of the field suffered most severely. The troops alongside them having given way, they were surrounded in a narrow space and cut down fighting hand to hand; some of the Athenians also fell into confusion in surrounding the enemy and mistook and so killed each other. [4] In this part of the field the Boeotians were beaten, and retreated upon the troops still fighting; but the right, where the Thebans were, got the better of the Athenians and shoved them further and further back, though gradually at first.

Outflanking had proven to be more effective than depth; the Athenian left, despite being driven back, had held together, presumably in expectation that their victorious right would sooner or later turn the tables.  But the Theban commander had moved two cavalry squadrons from his right wing, and ...

... their sudden appearance struck a panic into the victorious wing of the Athenians, who thought that it was another army coming against them. [6] At length in both parts of the field, disturbed by this panic, and with their line broken by the advancing Thebans, the whole Athenian army took to flight.

The flight of the Athenian right was accompanied by the collapse of the Athenian left.  Either the Theban pressure had proved too much, or the sight of the right in flight had broken the left's resolve.  I suspect the latter.  If so, the moral would seem to be that troops will hold out while there is hope, even if they are being forced backward.  And discipline may substitute for hope.

[Justin Swanton]

With hoplites, where interlocking shields are a crucial part of the formation, any kind of falling back or recoiling is out of the question. Your shield edge, overlapping the edge of a neighbour's shield, makes it impossible for you to give ground. So hoplites don't fall back. The defeat of a hoplite line seems to depend on a) getting outflanked; b) physically being forced back by a deeper opponent; c) seeing fresh enemy appear at the flank/rear. Any exceptions to this?

The absence of falling back would make a hoplite line particularly effective as the interlocking shields cancels out a natural panic trigger: file leaders giving way before better opponents. But it does make me wonder how hoplites would manage against a looser formation like a legion where individual legionaries are able to fall back to avoid blows if need be. Could this be the reason why the legions were able to smash through Hannibal's centre at Trebia even though they were up against his hoplite-armed best troops (who had uphill advantage to boot)?

[aligern]

Isn't there some doubt that the Africans at the Trebia are equipped as hoplites?? They may very likely have been thureophoroi and more lije an armoured version of the Spanish scutati??
Roy.

I think its a good point re Roman flexibility that they can fall back gighting, but aren't there exampkes of hoplites and pije bearing phalangites doing this over a long distance.
Against Caesar the Helvetii appear to have locked shields and yet fallen back over a considerable distance against the Romans.

Being closely formed is no hindrance to falling back, often quite a considerable distance.
Roy

[Prufrock]

A thing I've noticed from being in contact sports teams such as rugby union or rugby league, from playing rougher games such as bullrush, from participating in mass playfights at school lunchtimes, acorn / clod wars as a kid, participating is mass tug-of-war bouts, or dealing with potentially dodgy situations in bars, is that there are always some people in a group who are more up for the aggressive stuff than others, and those who are not quite so full of fire tend to rely on those madder types to do the hard work for everyone. They are not necessarily the leaders, but they are the guys who set the tone.

From playing school and club rugby of various types you know that if your tougher guys are getting a battering and they can't contain the tougher guys on the other team then those who are not quite as into risking hurt for the cause start looking around and thinking oh-oh, we could be in for it here, and that attitude can get infectious. If something doesn't turn that around, rather than thinking of winning, people start thinking of damage limitation, so some guys start to stay out of the contact areas, shy away from making tackles, and basically don't really want to know. The earnest, middlingly aggressive guys who are kind of up for but can't turn the tide on their own have to do more work, get exhausted faster, and once they're exhausted too, it gets really messy.

In games like bullrush, once the number of tacklers reaches a certain point, less enthusiastic people start thinking they are going to get hurt, and those who are not keen on that idea might run towards a weaker tackler or fall over to avoid getting hammered by one of the more fearsome practitioners (ie, give up).

In tug of war, when your anchor guys are grimacing, running out of puff and getting pulled forward, the whole group can quickly lose it. In acorn or clod wars, the guys who keep coming tend to make everyone else run away, so if you don't have people to match their aggression it's a short battle.

I imagine armies probably have similar sorts of dynamics, and if you can see that their tough guys are getting the better of yours, and your tough guys start to go down or out, a sinking feeling probably sets in. As a group you can probably stick it out for while with your middlingly aggressive guys in the hope that events elsewhere might turn in your favour, but if it's apparent no one else is coming to bail you out, I imagine there would come a point when some shock will occur, and mental and physical exhaustion will cause some to go, and once they go a more general disintegration of morale. There would be some of the tougher / more stoic middling guys who through pride or bloodymindedness would still stand in place, and the earlier runners might feel those guys will give them a chance to get away, which, if the survival instinct suddenly trumps the social instinct, probably gives an incentive to be one of the earlier runners.

But this could be quite wrong - contact sports are very different from battles, and my imagined psychological parallels could be quite spurious!

[aligern]

That fits happily with my category of 'Things not going as expected' . You don't expect your tough guys to fail and the concern at seeing them relling back would spread.
However,armies have mechanisms to cooe with this. They have junior leaders whose job is to lead abd inspire. They have discipline which makes the consequences of running a lot less attractive. Who wants to be known as the man who abandoned his leader, loyalty group or tribe on the battlefield? They have a stoic sense of duty. If Justin were to see Patrick fall then he girds himself to step forward. into the breach  :-)) .
The difficulty with spirts and childhood games analogies is that they have very different social mechanisms from a real battle. Turning up for a tax duty may be one way to characterise an ancient army's composition, but mostly the warriors are professional or semi professional and tied in by group and personal loyalty links and by a powerful social cohesion. These men are, as I said fighting as part of small teams that have roles within the team , that includes that the team know that if Patrick is stricken its Justin that comes forward and Holly that seconds him with Tim pushing forward to replace him .
Roy ( In a litter on a hill in the rear) .

[Prufrock]

True Roy: in professional armies the guys who really don't want to be there have probably either been weeded out or are back in camp digging. But there is still a pretty strong social code in sports and in school days (high school anyway, which is the period I'm thinking of). No one wants to get a reputation as a whuss, a sissy, or for being useless, so there are social costs, even as kids / or in social leagues.