The Makedonian phalanx -- why such depth?

[Paullus Scipio]

Paralus/Michael wrote:

This would be the third time Appian (or Polybios) has pointed out Antiochus’ error in cramping up the phalanx 32 deep. Evidently this is how it fought in the battle. Evidently the “friends” thought that divisions of 16 deep – stretching the line – will have far more useful.

...it always pays to try to work out frontages when trying to reconstruct particular dispositions in a given battle. At Magnesia, even with the 'double depth' phalanx, Antiochus' phalanx had a front of over 3 km, compared to the Romans 2 km or so, giving him a comfortable overlap. ( and he knew that in 'triplex acies', the Roman Heavy infantry were a total of 30 men deep - by Greek measure of depth in open order, including the reserve 'Triarii). Had Antiochus formed up 16 deep, his front would have been way too long and the flanks would have been out of the action, along with many of the Infantry phalanx, nor would he have had any 'reserve' and only half the 'weight' of the Roman formation...).

Antiochus' "friends" were plainly wrong and trying to apply 20-20 hindsight, and Antiochus, no military fool, was right. Doubtless he knew the phalanx was too deep to be fully effective ( whether it fought 32 deep, or under my hypothesis 16 deep), but it was still the best formation in the circumstances.

Just on Polybios. Agesilaos points out to me (not from this forum), quite rightly, that his audience was in great part Roman. Romans, then, are expected to be thoroughly familiar with phalanx tactics and that 16 always “closed up” to eight so as to fight?

Perhaps that’s why Polybios felt the need to finish off his discourse on the phalanx – for those who already well knew(?) – with the already quoted line about the force of its charge when 16 deep?

...I'm afraid your friend Agesilaos is probably mistaken in this instance. Polybius wrote in Greek for a Greek audience, at a time when few in Rome spoke Greek, and his purpose was to explain to the Greek world how Rome had come to dominate the Mediterranean world in such a short time. As he himself said:
"What man is so indifferent or idle that he would not wish to know how and under what form of government almost all the inhabited world came under the single rule of the Romans in less than 53 years?" [220-168 BC] Polybius I.1 ..and, for example...
" Now were we Greeks well acquainted with the two states which disputed the Empire of the World, it would not perhaps have been necessary for me to deal at all with their previous history" Polybius I.7. Clearly he is addressing Greeks. Only much later did Romans come to appreciate his work, when Phil-Hellenism took hold in Rome.
As to why he sometimes expounded on matters military, it was likely because his Greek audience, while well educated ,were not largely military men, but he still used the normal 'conventions' of Greek writers, in my view.

Another question. Just how deep was the “mixed phalanx” of 16 per file going to fight? Arrian mentions no 'half file' leader. If a 'half file' leader did exist - as might be demonstrated by Alexander stretching his line at Issos - that would only serve to indicate that the normal file depth for fighting was 16.
Another passage for thought.

...You are here trying to compare chalk and cheese. The 'new' and 'mixed' phalanx was an intended experiment that was never actually done.The idea was that the front three ranks would be 'sarissaphoroi', backed up by twelve ranks of Persian missile armed troops, with a rear rank of Macedonian file-closers to keep them in ranks and prevent runaways. No 'half-files', because it was not a pure hand-to-hand formation - only the front three ranks fought this way, supported by the missile troops shooting overhead, so this formation was intended to fight 16 deep. Note that any more than 3 ranks of sarissaphoroi were considered ineffective and un-necessary, and the hand-to-hand element would have fought just 3 deep. That seems a little thin, and significantly none of the Successors adopted it......The old phalanx continued to form up, under my hypothesis 16 deep in open/'normal' order, and actually fight 8 deep - plenty to provide a solid line, with 5 ranks actually taking part....

I would presume that this was the depth in which they fought given Livy's description - unless he is presuming that his readers knew that the phalanx would "halve its depth" to 16 when closing up for action?

...Livy was writing around 150 years after the event, and he drew on Polybius or other Greek writers. He may or may not have known exactly what Greek writers meant when they said "16 deep". Incidently, a Roman line of Hastati or Pricipes formed up usually 10 deep in 'open' order, and threw pila, before closing up to 5 deep for hand-to-hand combat, in my view - but this was done by ranks, not files ( see Warry "Warfare in the Classical World" p.112 where I diagrammed this...)

I emphasise the following:
1. We are NEVER told that the Macedonian phalanx actually fought 16 deep, the only express statement of them in battle (Issus) says "8 deep"and the manuals give drills to form 8 deep in close order....

2. We are NEVER told that Hoplites actually fought "8 deep" or "12 deep" etc - Xenophon speaks of 'battle formation' 4 deep, or of Spartans nominally 12 deep as "6 deep"....