degradation of Greek cavalry in Hellenistic era

[Sean Manning]

I am not sure you are being 100% fair. How often did Alexander face large armies equipped and trained as well as the armies fielded by the Diadochi? Lets be honest, beyond the Greek mercenaries and porbably the "Immortals" the Persian Empire deployed infantry that was little better than rabble compared to Alexander.

That's a strong statement. Other than the battles against Alexander, how much do we know about the effectiveness of Darius's troops? Persian infantry fled quickly at the Granicus, had some successes and some failures at Issos, and we can't tell how they fought at Gaugamela because our sources don't discuss it. They also gave Alexander a hard time in sieges and at the Persian Gates. Persian troops (like Gauls in Caesar's day) could have been fairly good soldiers without being able to beat a smaller army of veterans under brilliant leaders.

When did Persian trooops meet up against Macedonian troops and survive? Persian troops could defeat Greek hoplites but not in head on engagements. The simple truth is that infantry, especially heavy infantry, was not the core of the Persian army.

The Persian Gates and Issos. Judging by Arrian, the hoplites who were giving Alexander's phalanx a hard time at Issos were a mix of Persians and Greeks. But then Alexander attacked them in the flank (after routing Persian troops of some kind), Darius fled, and the Persian army broke up. At the Persian Gates the defenders did better than the army of Thracians which tried to roll down carts on Alexander's men as they attacked another pass.

In the 6th and 5th centuries, the Persian army was based on infantry. In every land battle of the Persian Wars, the decisive point was a clash of infantry. Sometimes the Persians attacked first, and sometimes the Greeks did. Cavalry grew more important as time passed, but Darius still gave infantry a prominent role at Issos and Gaugamela. Drifting back on topic, Alexander's battle plans also depended on all parts of his army, even if he and his cavalry get most of the glory! But I agree that because he and his army were so much better than their opponents, he could do things which his successors struggled to match.