Hey! So am I! I guess you were a member of the RTR team, since you brought it up? Cataphracts were adopted relatively early; they were already in existence during the 2nd century CE, although only in small numbers. Actually, many armies of the Germanic states of the Dark Ages/Early Middle Ages used cavalry consisting almost entirely of heavy, charging cavalry (eg. proto-knights). Some of the early expeditions sent by the HRE (when it was still the eastern half of the former Frankish empire) against the Magyars in the 9th century or so were almost entirely of heavy cavalry.