The Makedonian phalanx -- why such depth?

[PMBardunias]

I have not yet turned to the subject of 'optimum depth', or why given two roughly equal bodies of Hoplites, those 4 deep in close order would generally beat those 8 deep in close order.

This I would like to hear :wink:

Then there are the difficulties/impossibilities of moving lines of men, a kilometre long, across typical Greek terrain in 'close order' ........( c.f. Polybius' criticisms of Callisthenes referred to ante)

I think there is ample evidence that they did not do this. They moved a group of units that start off in a rough line at close order, but the many examples we have of units charging at different distances show that there was no expectation to move the whole line in marionette unison such as we might expect from the early modern armies where drill was fetishized. The most gross example of this is that any unit lined up along side Spartans could not have kept pace with them because they marched during the charge while even Spartan trained mercenaries ran. This is not such a problem because a battle line reformed upon contact with enemy units and exploiting such differential arrival times is a lot more difficult for an enemy to do that it appears to us.