[Tomsdad]

Originally Posted by tshiggins

I double-checked, and you're right. The Parthian nobles fought as armored cataphracts, and the archers were light cavalry.

Interestingly, neither used stirrups, at the time.

Originally Posted by Ulzgoroth

My research seemed to indicate that in some periods the cataphracts were archers as well as heavy lancers. Though they were certainly separate from the light horse archers.

There's cultural aspect here as well, in that part of the world horseback archery was very much part of a noble's skillset.

So there would be some crossover in potential use. But I'm guessing it was a matter of intended role in a battle.