Along the way he introduces us to Odysseus’ bow (with a quotation from the Odyssey (where Penelope tells the suitors that whoever strings the bow and shoots through 12 axes [that's important] can carry her away from her home)). [Important because he'd not only have to string the bow to full strength, but draw and loose 12 arrows.]

From there it’s off to different kinds of bows and how they’re strung, and how much energy they can store (in Odysseus’ case, lots), and the difference between the regular bow and the compound bow, favored by the Parthians.

“The Parthian bow was handy enough for the cavalrymen to be able to shoot backwards, as they retreated, at their Roman pursuers; from this we get the phrase “Parthian shot”. (p.83)

The key, of course, is whether the Romans called the Parthians “Parthians”.

Has anybody checked the OED?

My issue with “Parthian shot” being the original is twofold:

* Spotty 19th-century bookkeeping aside, “parting shot” appears in print nearly a quarter of a century before “Parthian shot”, and
* The Parthians’ tactic was not to fire arrows behind them while retreating (in other words, a last salvo before leaving the field); it was to feign retreat so that their enemies would follow them (with their defenses lowered, since a retreating enemy couldn’t possibly attack), then shoot behind them, thus not only wounding their enemy but drawing them closer to the main body of the Parthian army.

Moreover, people have had nearly two millennia to discuss the Parthians. One would assume that “Parthian shot” would have come up sooner had it actually been used in earnest to describe the situation in question.

It seems far more likely to me that “parting shot” is the original, some 19th-century Classics major saw the opportunity to make a pun, and the “Parthian” joke was repeated until people were confused.