The Gauls did not reason. Seeing only the inflexible line, they bound themselves together, thus rendering relief impracticable. They believed, as did the Greeks, in the power of the mass and impulse of deep files, and did not understand that deep files were powerless to push the first ranks forward as they recoiled in the face of death. It is a strange error to believe that the last ranks will go to meet that which made the first ones fall back. On the contrary, the contagion of recoil is so strong that the stopping of the head means the falling back of the rear!
The Greeks, also, certainly had reserves and supports in the second half of their dense ranks. But the idea of mass dominated. They placed these supports and reserves too near, forgetting the essential, man.
The Romans believed in the power of mass, but from the moral point of view only. They did not multiply the files in order to add to the mass, but to give to the combatants the confidence of being aided and relieved. The number of ranks was calculated according to the moral pressure that the last ranks could sustain.
There is a point beyond which man cannot bear the anxiety of combat in the front lines without being engaged. The Romans did not so increase the number of ranks as to bring about this condition. The Greeks did not observe and calculate so well. They sometimes brought the number of files up to thirty-two and their last files, which in their minds, were doubtless their reserves, found themselves forcibly dragged into the material disorder of the first ones.
In the order by maniples in the Roman legion, the best soldiers, those whose courage had been proved by experience in battle, waited stoically, kept in the second and third lines. They were far enough away not to suffer wounds and not to be drawn in by the front line retiring into their intervals. Yet they were near enough to give support when necessary or to finish the job by advancing.
When the three separate and successive maniples of the first cohort were united in order to form the united battle cohort of Marius and of Caesar, the same brain placed the most reliable men in the last lines, i.e., the oldest. The youngest, the most impetuous, were in the first lines. The legion was not increased simply to make numbers or mass. Each had his turn in action, each man in his maniple, each maniple in its cohort, and, when the unit became a cohort, each cohort in the order of battle.
We have seen that the Roman theory dictated a depth of ranks to furnish successive lines of combatants. The genius of the general modified these established formations. If the men were inured to war, well-trained, reliable, tenacious, quick to relieve their file leaders, full of confidence in their general and their own comrades, the general diminished the depth of the files, did away with the lines even, in order to increase the number of immediate combatants by increasing the front. His men having a moral, and sometimes also a physical endurance superior to that of the adversary, the general knew that the last ranks of the latter would not, under pressure, hold sufficiently to relieve the first lines nor to forbid the relief of his own. Hannibal had a part of his infantry, the Africans, armed and drilled in the Roman way; his Spanish infantrymen had the long wind of the Spaniards of to-day; his Gallic soldiers, tried out by hardship, were in the same way fit for long efforts. Hannibal, strong with the confidence with which he inspired his people, drew up a line less deep by half than the Roman army and at Cannae hemmed in an army which had twice his number and exterminated it. Caesar at Pharsalus, for similar reasons, did not hesitate to decrease his depth. He faced double his strength in the army of Pompey, a Roman army like his own, and crushed it.
We have mentioned Cannae and Pharsalus, we shall study in them the mechanism and the morale of ancient combat, two things which cannot be separated. We cannot find better examples of battle more clearly and more impartially exhibited. This is due in one case to the clear presentation of Polybius, who obtained his information from the fugitives from Cannae, possibly even from some of the conquerors; in the other it is due to the impassive clearness of Caesar in describing the art of war.