A Parthinian (Parting) Shot: Origin and Meaning

A program on the History or National Geographic channel, I can’t recall which, covered the demise of the Roman Tribune Marcus Crassus at the hands of the Parthinians. The focus of the documentary was the fate of the survivors of the 7 Roman Legions that were soundly thrashed in a battle, after which Crassus lost his head, so to speak. It would appear as though the survivors were spirited off to China somewhere and evidence of Roman architecture is still to be seen there today.
Anyhow, the statement that caught my attention was a reference to the saying a “Parthian shot”, which was given as the origin of the modern saying “a parting shot”.
Firstly the concept of a Parthian shot. The Parthinians were excellent horsemen and really good archers. What they could do well was to shoot arrows while galloping along on horseback. (Reflex bows, invented by the Chinese, that were lethal up to a range of 500 yards, helped a lot)
Crassus made a number of military blunders in the final conflict, and his biggest mistake was to commit his infantry to charge at what appeared to be a retreating Parthian cavalry. This was a ruse, as the Parthinians created the impression that they were on the run, and when the Romans charged to finish the enemy off, they were met with a devastating barrage of arrows fired “backwards” from the mounted cavalry. End of the battle for the Romans. According to the TV program this was not part of the Roman standard operating procedures of fighting battles. When you run away from battle it is a sign of capitulation, not retaliation. Not fair etc etc.
Now we get to the dictionary definition part.
“The Parthinian horsemen were accustomed to discharging their missiles backwards when in real or pretended flight, hence used allusively in a Parthinian shaft, shot or glance”
Now the parting shot part. I thought that Parthian shot morphed into parting shot with the passing of time. Although there are references supporting this, there is another school of thought that maintains a parting shot is a saying in its own right and originated from things naval. (If you scratch around on the Internet you will find more).
The focus of this post is the Parthian part, will look at the parting part a bit later
You wound, like Parthians, while you fly, And kill with a retreating eye. (Samuel Butler 1678)