The Makedonian phalanx -- why such depth?

[Paralus]

....here and elsewhere, IIRC, you evidently have doubts about the Macedonian Phlanx forming 'synaspismos' on a one cubit frontage, as have others. As long ago as 2000 Connolly put together 16 re-enactors with pelta and sarissa to test various problems. The results , complete with photos, were published in JRMES 11 2000.
Here is what he had to say about forming synaspismos:-
"Doubling the files proved far easier than expected. Formed up in the two-cubit formation (close order/pyknosis) with pikes in the upright position....[the file] ...came up the interval between the other two files. They then levelled their pikes proving it was possible to 'double' the formation allowing only one cubit per man".

No, I have no problem with synaspismos and the Macedonian phalanx. I would think that more than 16 re-enactors would be needed to perfrom a proper test of the system though.

As for how it was done at Hydaspes, I venture to suggest that the rear Half-files simply closed up as Connolly described - this could occur while fighting was occurring , for the enemy line would be beyond the hedge of pikes, or perhaps more likely, during one of the various lulls when the two sides will have drawn apart to draw breath and reform.

As opposed to Connolly's single file above, the phalanx at Hydaspes was - by all accounts - heavily engaged in a battle of life and death. Unless Alexander ordered his phalanx to disengage in the heat of battle, retire and then raise sarisae so as to allow Connolly's "easier than expected" synaspismos, I don't see it. You are arguing for a rear four to insinuate itself amid engaged files. If more than four sarisae were lowered in the attack (closed up) position, then one rank has to raise their sarisae.

I doubt Alexander had his pahalnx disengage as he was in the process of surrounding the Indians at the time. Hence the rear "quarter file", on your hypothesis, will have had to move up between four ranks of engaged sarisa wielders. That these files were so neat as to allow same - given the descriptions of the combat - is unlikely. In fact, reading between the lines and ignoring Macedonian propaganda, there was some serious loss of life in the infantry ranks. Not a few of your half files may already have been "quarter files" before any supposed doubling down to syaspismos.