The Makedonian phalanx -- why such depth?

[Sean Manning]

Yes, that is one of the three manuals I was referring to ( Aelian, Asclepiodotus and Arrian).....each author's work is very similar and all appear to be based on a single 'lost' original Hellenistic work. As is known from more modern drill manuals, (e.g. Prussian) a single line of 'file closers' is sufficient to co-erce/prevent runaways, and as the manuals state, three is more than sufficient to 'lean/push', along probably with ranks 2-5, as and when necessary. This 'othismos' probably occurred as both sides tired and the sarissae were, for the most part, embedded in the enemy shields.......

Well, it looks like Aelian thought that the file-closers could use some help! Two to four ranks seems to have been sufficient for infantry fighting with muskets and rifle-muskets, but they didn't engage in prolonged hand-to-hand combat. Combat at a distance is different from hand-to-hand combat and is probably psychologically easier. There is an interesting comment in the Strategikon of Maurice that two or three ranks of cavalry would maximize fighting power, but in practice 6-10 are needed because there are only so many brave men on good horses able to fight in the front ranks successfully. I should do some research on pike formations in other cultures, but I don't think a depth of 16 is particularly unusual.