The cataphract was the heavily armored cavalryman who formed a core element of Byzantine military power.
Cataphracts protected both rider and horse with extensive armor and carried long lances, swords, or bows. Their armor made them slower than lightly equipped cavalry, but it allowed them to survive close combat and smash into enemy formations. They were often used in disciplined wedge formations designed to create gaps in opposing lines.
The Byzantine army inherited and developed the cataphract tradition from earlier Iranian, Hellenistic, and Roman military practices. Byzantine commanders combined these heavily armored horsemen with archers, infantry, and lighter cavalry rather than treating them as a completely independent force. Their tactical value was greatest when coordinated with other arms.
The term is sometimes loosely equated with the medieval European knight, but the two were not identical institutions. Cataphracts belonged to a broader eastern military tradition, and Byzantine heavy cavalry continued to evolve into forms such as the klibanophoroi. Western mercenary cavalry eventually became increasingly important in the later empire.