The Makedonian phalanx -- why such depth?

[Paullus Scipio]

Paralus wrote:

Paullus places far too much faith in a sainted Xenophon.

...I don't think one can disparage Xenophon by such scorn. Let us remind ourselves that he was an experienced General and so knows what he is talking about. He is also our only source who gives us detail of Hoplite drill and formations. I prefer what he has to say on the subject, rather than the meaningless opinions of modern "armchair generals" who have never themselves even taken part in military formations/drills, let alone have any practical knowledge of ancient warfare as Xenophon does. Which is not to say that I read him uncritically in all respects.

I agree for the most part with what you say about his political bias ( for those who want to know more, I recommend "Xenophon" by J.K. Anderson publisher Duckworth &co ltd 1974 ISBN 0 7156 0702 2). I don't agree with you that the reason Xenophon, an expert General, forbore to comment on Theban tactics was because they were "too difficult to write down". Rather his political leanings did not allow him to be dispassionate, and if something pained him he chose not to write of it, or not provide detail, as, for example he writes of the brilliant little cavalry action that his son died leading, but forbears to mention Gryllus by name....
Lastly, the Spartan attempt to outflank and envelop ('anastrophe')probably did not involve any 'thinning' at all ( the Spartans weren't tactically imbeciles). Although Arrian in his tactical manual (9.5) refers to extending the phalanx by thinning, Plutarch's version is different. Lazenby hypothesised that in fact the 'folding back'( anastrophe) involved moving troops from the un-engaged left of the Spartan contingent to the right for this purpose, so that Cleombrotos was attempting what Agis at Mantinea attempted, and perhaps the Spartans were also trying to increase their depth. It is hard to discern exactly what the Spartans were attempting to do, because they never got to complete their manouevre thanks to Pelopidas charging and disrupting it, and Cleombrotos didn't survive to explain.....

.....and the confusion surrounding what the Spartans attempted to do may be why Xenophon does not speculate on the matter, as well.