The Makedonian phalanx -- why such depth?

[PMBardunias]

You seem to be conflating two separate accounts of Xenophon here. The reference to practising Drill while marching to Dinner in a large mess-tent is from the quasi 'factional' Cyropaedia (II.21-23)...and I'm quite sure you don't believe for one minute that the purpose of the Drill practise was to proceed to Dinner in an orderly fashion!!!
If you do hold such a belief, it should be dispelled a little later. Xenophon is at pains to have Cyrus show leadership by rewarding with a feast those company captains who use every opportunity to drill their men, including going to dinner ( which is still the practise in most militaries today). A captain tells Cyrus he drills both getting to dinner, and in reverse, leaving dinner.

You mentioned both quotes above. Of course the idea was to get his men to dinner, for that is what he was doing. He may have been doing it in the same manner he would have formed for battle, but because at worst he faced an irate chef or two :oops: he was free to double down to 6- something that was within the tactical repertoire but not something that had to be done. They could simply stop at the 12 rank stage and form close, thus preserving depth if they wished. Surely you don't think this beyond their skill.

We are here concerned with the 'norm', or what is typical. We are told that Spartan 'platoons' typically of 36 men ( depending on the age-groups called up) could form up in (probably) single file, threes (12 deep) or sixes( 6deep).

My point is that there is no "norm" look back at the numbers of ranks we see in battle descriptions, they are all over the place. When we read of spartans being able to form in 12 or 6 its stands tro reason that they do it by cutting short the doubling process. To me this makes much more sense than labelling the penultimate double and assuming he really means 6 and 3.

No other depths are mentioned - no "sometimes 50, sometimes two". What you say is theoretically possible, but not what Xenophon says.

Of course he does. He mentions 4, which means also a stage with 8, 16 or 24 if tripled and 32 or 48 at Cilicia. He mentions 6 and thus 12, 24, 48 at the dinner drill. He implies 6, 12, and 36 in the Lak. constitution. He mentions 50, probably 48 and some hangers on, in relation to Thebes and they had to have some means of forming at this depth. If we jump authors, then Thukydides mentions 25 at delium, which is convieniently half of 50 and thus may mean that Epaminondas simply stopped the process sooner. He mentions the Orthoi Lochoi formation, surely they could have formed this with no gaps between lochoi to get a deep phalanx.

The process of simply stopping the doubling at whatever depth you require and forming in close order at that depth seems to me about as simple an explanation as you could have for how they arrived at all these different depths- especially the real deep ones which just happen to be divisible into the usual file sizes. The fact that units were expected to be able to form in different depths- for example the Thebans were not to form deeper than 16 during the Corinthian war by treaty, but did anyway- tells us that depth cannot be slavishly tied to unit size, but had to be decided on the spot.

Remember that each platoon/enomotia, once drawn up in Phalanx cannot change its front, so all manoevres must be carried out by thinning or deepening the line, just as Xenophon says.
In order that readers can visualise what is happening, I'm including the schematics I sent you some time ago - that way our discussion will be easier to follow.

Any formation a phalanx can get into they can get out of. They can simply "undouble" prior to a countermarch if they need the space.

Note that in 'normal/open ' order, in which they manouevre, (such as Laconian countermarch - essentially what a High school band does to reverse course) the formation is 8x8 in the Cyropaedian drill, and the depth of the 'normal' formation is correctly described as 8 deep. However, my hypothesis is that the final Charge was carried out in 'close' order of half-files - in which formation manouevres such as Laconian counter-march could not be carried out. ( and not just mine - compare similar ideas in Connolly P. and Anderson J.K. ) Once the Phalanx 'closed up', it was committed and could only move forward/back ( except for the famous 'rightward drift')

Or undouble back to 4x16 if they need lanes, then redouble.

My point is simply to counter the "special pleading" argument that when Xenophon talks of customary battle formation being 4 deep, he is speaking of an especially thin one used only against Asiatics. Given knowledge that a "thin" centre failed at Marathon, the Ten Thousand will hardly have "thinned" their formation, ergo the "customary Battle formation" is just that !

But I agree with your point. Given that a line of probably 4 or 3 failed and was broken through by lightly armed persians, it would be suicidal to form 4 deep to face hoplites. There are few contexts were such shallow depths are mentioned for actual battles (as opposed to shows and dinner theatre) and usually there is an explanation- like the Spartans at the long walls trying to extend their line as far as possible.