The Makedonian phalanx -- why such depth?

[PMBardunias]

I'll preface this by saying that there are few if any "Innovations" at thebes in this period. What there was was an excellent use of tactical elements that originated with earlier Thebans, Spartans, and others.

The deep phalanx is only one of these elements. The efficient use of combnations of multiple troop types, specifically the integration of cavalry and infantry, was perhaps just as important.

The deep phalanx itself was a means of countering the higher quality of the spartan hoplite (though its origin is Pagondas breaking through the Athenian phalanx at Delium). The lesson that Phillip may have learned was simply to use unorthodox means to counter hoplites of better quality. Thus we see the birth of close-packed ranks of sarissa armed men who outreach the hoplite and make pushing against their spear points hazardous for the greeks.

Also, recall that there was a tie between Phillip and Iphicrates, who also used unorthodox solutions to create hoplites out of lesser quality troops. Though I must admit that I have come to doubt the direct descent of sarissaphoroi from Iphicratids.