Heavy cavalry was a class of cavalry intended to deliver a battlefield charge and also to act as a tactical reserve; they are also often termed shock cavalry. Although their equipment differed greatly depending on the region and historical period, heavy cavalry were generally mounted on large powerful warhorses, wore body armor, and armed with either lances, swords, maces, flails (disputed), battle axes, or war hammers; their mounts may also have been protected by barding. They were distinct from light cavalry, who were intended for raiding, reconnaissance, screening, skirmishing, patrolling, and tactical communications.
Military of the Sasanian Empire and Cataphract
Iranian tribes such as the Massagetae were believed to be the originator of the class of heavy cavalry known as cataphract. During the time of Achaemenid Persia cavalry was the elite arm of service (as was the case in most civilizations), and many Persian horsemen such as the bodyguard unit of Cyrus the Younger were rather heavily armoured by the standards of the era. By the time of Alexander's invasion cataphract units with both men and beasts being fully encased in armour were already in use by the Persians.
The Parthian Empire of Ancient Iran marks an early recorded utilization of armoured cavalry in warfare, and are specifically believed to have given rise to the tradition of very heavily armoured cataphract lancers. These had a distinct role from ordinary heavy cavalry and were primarily used as an elite assault force, to pummel infantry formations into submission, or even acted in a dual-purpose role as horse archers and cataphracts.
Ammianus Marcellinus, a Roman general and historian who served in the army of Constantius II in Gaul and Persia, fought against the Persians under Julian the Apostate and took part in the retreat of his successor, Jovian.