The Makedonian phalanx -- why such depth?

[Paralus]

I'm afraid that passage of Thucydides (V.66 onward) is not as revelationary as you might think. At the stage of the battle Thucydides is describing the armies 'drawn up', unit by unit.

Rubbish. The allied army is clearly described as “in battle order”, the order in “which they meant to fight” were they to be confronted by the very near enemy. They clearly were not about to be executing any intricate movements.

There is little doubt that the Spartans – surprised by both the enemy’s order and proximity – formed up in similar fashion.

Thus a Spartan enomotia(platoon) of 32 would be drawn up in 4 files of 8 deep, which is 8 ranks, just as Thucydides says.

No, you confuse “files” (depth) with “ranks” (breadth). Clearly ranks of "four" are those at the front. Thucydides makes this plain as day when he states that the “front rank” consisted of 448 men. This, clearly, cannot be a “rank” 448 deep.