Sniper is correct. (Thanks for making this thread by the way, and speaking of which I'm going to re-read my polybius...) The infantry was what made Alexander the conquerer of Asia. It put the 'Great' in his name.
Without the coehsive force of the infantry nearly all of Alexander's victories would have been impossible. His defeat of Darius was not due to cavalry, but becuase of his phalanx.
The Battle of Granicus for example:
The battle started with a cavalry and light infantry feint from the Macedonian left, from Parmenion's side of the battle line. The Persians heavily reinforced that side, and the feint was driven back, but at that point, Alexander led the horse companions in their classic wedge-shaped charge, and smashed into the center of the Persian line. The Persians countercharged with a squadron of nobles on horse, and accounts show that in the melee, several high-ranking Persian nobles were killed by Alexander himself or his bodyguards, although Alexander was stunned by an axe-blow from a Persian nobleman. Before the noble could deal a death-blow, however, he was himself killed by Cleitus the Black. Alexander quickly recovered.
The Macedonian cavalry then turned left and started rolling up the Persian cavalry, which was engaged with the left side of the Macedonian line after a general advance. A hole opened in the recently vacated place in the battle line, and the Macedonian infantry charged through to engage the poor quality Persian infantry in the rear. At this, both flanks of the Persian cavalry retreated, seeing the collapse of the center. The infantry also routed, with many being cut down in the rout.
Total casualties for the Macedonians were anywhere between 100 and 200. The Persians had 2000 infantry captured, roughly 1,000 cavalry and 3,000 infantry killed, mostly in the rout.
Here it is shown that it was the infantry that carried the day. So, its not that either the infantry or the cavalry were better or more important than the other, its rather that both were supremely well trained and effective troops that Alexander used in concert to turn his campaign into victory. The two units complimented each other in battle.
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Onto the subject of the post. Here Sniper, you can see why it is that I said the Roman tri-line was so effective against a phalanx and superior to it. Its flexibility. It was this that allowed the Romans to win so many victories.
