Can I disagree on the psycho front? One lesson learned from Kendo training is that the violent and indisciplined struggle to learn any meaningful fighting techniques as they cannot control themselves, and they dont last too long if faced with a person who has command of technique. The Legions relied on men acting in accord and with pre-determined strategy, witness Caeser commenting on his men not wasting time by going to their own standards but moving behind the nearest standard when suddenly surprised.( Ill try and find the full reference )later. I also note one or two examples of extreme fire discipline , the opposing veteran Legions at Forum Gallorum raised no war cry knowing it would not terrify their veteran opponents(Appian: Civil War);at Pharsalus Pompey told his men to hold position and await attack to reduce the impetus of Caeser's attack,Ceaser's men spontaneously checked their charge so as not to waste energy in the first assault.
I can understand men cracking with pent up fury battle stress and cutting down fleeing enemies, time and again this is the fatal episode in many ancient (and modern) battles and seems to be an imprinted reflex to destroy when the enemy turns his back in combat. I can also see that there is nothing deadlier than disciplined and hardened troops let off the leash, the Icenii casualties were unbelievable,including oxen cut down in their traces never mind the camp followers whod turned up to watch the show.
I also have a reference to the British Legions "singing their victory hymm".
Rambled on again
and the prospect of booty-before facing the Icenii the Romans were exhorted not to think of booty because if they triumphed "all would be theirs"