Something which puzzles me slightly is the fact that the Romans began to use Kataphraktoi long after they first encountered them. Supposedly, they were first deployed in the time of Hadrian and did not become common until the time of Gallenius. So I was wondering if anyone could offer insight in regard to the following:

Given that hellenistic states like the Seleucids and Bactria began to use Kataphraktoi after encountering them on the field of battle, why is it that the romans took so long to do the same? Did they ever attempt to deploy Hetairoi-style heavy cavalry? Did their allies ever provide either kind of cavalry?

When the rump Seleucid state was annexed by Pompeius, were there any hetairoi-style riders or kataphraktoi left with them?

Were there any abortive attempts to establish these kinds of units before Hadrian?