The Makedonian phalanx -- why such depth?

[Paullus Scipio]

....and it might be argued that sarissas would be of little use in a siege, being too cumbersome and that on such occasions ( in fact everything except major Battles) the sarissaphoroi reverted to the traditional Macedonian armament of two or more longche( short dual purpose throwing/thrusting spear).......which I think was the case.

Paralus wrote:

Quote:For since, when it has closed up for action, each man, with his arms, occupies a space of three feet in breadth […] The consequence is that while the pikes of the second, third, and fourth ranks extend farther than those of the fifth rank, those of that rank extend two cubits beyond the bodies of the men in the first rank, when the phalanx has its characteristic close order as regards both depth and breadth […] From this we can easily conceive what is the nature and force of a charge by the whole phalanx when it is sixteen deep. In this case those further back and the fifth rank cannot use their pikes so as to take any active part in the battle.

I'm afraid that the way in which you have condensed Polybius' words here is a little misleading. It may not be the case that Polybius has contradicted himself, because the reference to 'close order', and the reference to 16 deep occur in two separate paragraphs, and after describing close order in the first paragraph, in the second one Polybius has reverted to describing what I believe is the 'convention' among Greek authors to refer to depth in 'normal'/open order, and readers would know that such a formation would 'close up' as described in the manuals, and halve it's depth. Thus:
Poybius XVIII.29-30 ( translation courtesy of Bill Thayer's Lacus Curtius site)....Btw Book 17 that you give is lost in it's entirety... :wink:

29 That when the phalanx has its characteristic virtue and strength nothing can sustain its frontal attack or withstand the charge can easily be understood for many reasons. For since, when it has closed up for action, each man, with his arms, occupies a space of two cubits/three feet in breadth, and the length of the pikes is according to the original design sixteen cubits, but as adapted to actual need fourteen cubits, from which we must subtract the distance between the bearer's two hands and the length of the weighted portion of the pike behind which serves to keep it couched — four cubits in all — it is evident that it must extend ten cubits beyond the body of each hoplite when he charges the enemy grasping it with both hands. The consequence is that while the pikes of the second, third, and fourth ranks extend farther than those of the fifth rank, those of that rank extend two cubits beyond the bodies of the men in the first rank, when the phalanx has its characteristic close order as regards both depth and breadth, as Homer expresses it in these verses:

Spear crowded spear,
Shield, helmet, man press'd helmet, man, and shield;
The hairy crests of their resplendent casques
Kiss'd close at every nod, so wedged they stood.
This description is both true and fine, and it is evident that each man of the first rank must have the points of five pikes extending beyond him, each at a distance of two cubits( 3 ft) from the next.

30 From this we can easily conceive what is the nature and force of a charge by the whole phalanx when it is sixteen deep. In this case those further back than the fifth rank cannot use their pikes so as to take any active part in the battle. They therefore do not severally level their pikes, but hold them slanting up in the air over the shoulders of those in front of them, so as to protect the whole formation from above, keeping off by this serried mass of pikes all missiles which, passing over the heads of the first ranks, might fall on those immediately in front of and behind them. But these men by the sheer pressure of their bodily weight in the charge add to its force, and it is quite impossible for the first ranks to face about.

....in the first paragraph, he outlines the 'porcupine' effect of 'close order', and in the second he is referring to "a sixteen deep phalanx" i.e. it's normal formation as opposed to some other depth - again with all depths being referred to in 'normal'/open formation.