How Effective were Spears Against Cavalry?

[Nathan Ross]

According to Goldsworthy The Roman Army they could catch them because the Parthians, swollen with confidence after the defeat of Crassus, were convinced the legionaries would flinch as soon as they would make a charge towards them, and found out too late that they wouldn't.

Incidentally, there are several different accounts of this same battle (Gindarus). Besides Plutarch and Cassius Dio, there are the following:

The defeat was not inflicted without a stratagem on the part of the general, who, under a pretence of panic, allowed the enemy to approach so close to the camp that he prevented them from making use of their arrows by depriving them of room to shoot.
Florus, Epitome, II.XVIII

Ventidius, when fighting against the Parthians, would not lead out his soldiers until the Parthians were within five hundred paces. Thus by a rapid advance he came so near them that, meeting them at close quarters, he escaped their arrows, which they shoot from a distance.
Frontinus, Stratagema, II

Both of these imply that it was Parthian horse archers attacking the Roman position, and against whom the Romans made their counter-charge, not cataphracts (unless the latter were also armed with bows, of course...)

The Florus quote, interestingly, seems to contradict Goldsworthy's reading of the battle - rather than 'not flinching', the Romans deliberately feigned panic, thereby drawing the Parthians into an improvident attack. A tactic, in fact, not unlike the one mentioned by Nazarius, hmm...

In the same book, Frontinus describes what seems to be a different battle between Ventidius and the Parthians:

Ventidius... posted eighteen cohorts at the side of the camp in a hidden valley, with cavalry stationed behind the infantry. Then he sent a very small detachment against the enemy. When these by feigning flight had drawn the enemy in hot pursuit beyond the place of ambush, the force at the side rose up, whereupon Ventidius drove the Parthians in precipitate flight and slaughtered them.
(Stratagema, Book II)

Again, as in Zosimus' description of Emesa in 272, we have infantry attacking the flank of a cavalry force disordered by a provoked pursuit.

The action of topoi, perhaps? Or a suggestion that these kind of tactics were frequently used to defeat cavalry?

;-)