the likelihood of the result I now indicate requiring no argument but only the evidence of actual facts.
For the Romans do not make their line equal in force to the enemy and expose all the legions to a frontal attack by the phalanx, but part of their forces remain in reserve and the rest engaged the enemy.
Afterwards whether the phalanx drives back by its charge the force opposed to it or is repulsed by this force,
its own peculiar formation is broken up. For either in following up a retreating foe or in flying before an attacking foe, they leave behind the other parts of their own army, upon which the enemy's reserve have room enough in the space formerly held by the phalanx to attack no longer in front but appearing by a lateral movement on the flank and rear of the phalanx.
When it is thus easy to guard against the opportunities and advantages of the phalanx, but impossible to prevent the enemy from taking advantage of the proper moment to act against it, to one kind of formation naturally proves in reality superior to the other.
Again, those who employ the phalanx have to march through and encamp in every variety of country; they are compelled to occupy favourable positions in advance, to besiege certain positions and to be besieged in others, and to meet attacks from quarters the least expected.
For all such contingencies are parts of war, and victory sometimes wholly and sometimes very largely depends on them.
Now in all these matters the Macedonian formation is at times of little use and at times of no use at all, because the phalanx soldier can be of service neither in detachments nor singly, while the Roman formation is efficient.
For every Roman soldier, once he is armed and sets about his business, can adapt himself equally well to every place and time and can meet attack from every quarter.
He is likewise equally prepared and equally in condition whether he has to fight together with the whole army or with a part of it or in maniples or singly.
So since in all particulars the Romans are much more serviceable, Roman plans are much more apt to result in success than those of others.
I thought it necessary to speak on this subject at some length because many Greeks on the actual occasions when the Macedonians suffered defeat considered the event as almost incredible, and many will still continue to wonder why and how the phalanx comes to be conquered by troops armed in the Roman fashion.
Walbank Commentary