The Khûveshâvagân are in spite of their decline still an extra-heavy cavalry unit worthy of respect. Heavily armed and armoured the Khûveshâvagân are a full-contact unit intended to mount a terrible charge and to maul down lesser foes in melee thanks to their swords.
The Khûveshâvagân used to be the most expensively attired cavalry in the world, and were indeed the sign of the equestrian power of the Achaemenid world order. With the coming of Macedonian cavalry tactics, the Khûveshâvagân had undergone several changes. The final product was an extra-heavy cavalry unit, magnificently equipped with the finest technology mustered by the Achaemenids. Financed by the royal treasuries, they were made into a contingent of specific honour, The Kinsmen. Armed with a xyston, and a machaira along with the deployment in column formation, this unit was purely equipped for melee combat, like the later cataphracts. The mount being barded with peytrel, chamfrôn and the parameridia or armoured saddle, made this unit a particularly headstrong opponent worthy of respect.
With the royal treasuries withdrawn and the adoption of additional Macedonian conventions, the Khûveshâvagân are no longer "Kinsmen" per se. Only in appearance have most of the fearsome features been retained. Still heavily armoured they make a respectable contender, and a reliable heavy cavalry they are only truly inferior to the proper cataphracts in the matter of equipment and tactics. Armed with a xyston and a machaira this full-contact unit can mount a terrible charge, wreaking havoc upon the enemy and additionally being clad entirely in bronze and the horse being armoured with an exotic combination of chamfrôn, peytrel and the parameridia, it must certainly have been a most impressive unit, both an ornament to whomever affording these warriors and a fearsome enemy. However, the unit being in decline (Due to being financed by nobles rather than the royal treasury) and increasingly archaic vis-a-vis to the torrent of improved cavalry equipment being developed in the steppes, will make this unit only useful as an option of heavy cavalry before cataphracts can be fielded.
Historically, the late Achaemenian heavy cavalry was an amalgam between Iranian horsemanship and an increasingly higher need for resilient and headstrong cavalry for shock tactics. Chariots, in particular scythed were most fearsome with a ample support, specifically heavy cavalry. The cavalry reforms of the latter half of the 5th century reached its apex during the patronage of the Persian Commander-in-Chief Pharnabazus, distinguished through Xenophon as a capable general, where the Persian "Cuirassiers" were not lined up for close combat but rather organized in columns for a sustained momentum in a charge. In accordance with the relief of Bozkir and some clear depictions of a parameridia (The armoured saddle), and earlier mention of horse armour in the form of peytrel and chamfrôn (As a nose-plate), this cavalry must have been quite heavily armoured. This cavalry, other than being depicted as the bodyguard of Cyrus The Younger during the civil war of Achaemenid Persia, was about to get a second overhaul, a step closer to the heavily armoured cataphracts of later Iranian dynasties. By then, the Persian army was beginning to become more Hellenized, which included certain Greek sabres.
During 372 BCE, Datames replaced Pharnabazus as the Commander-in-Chief of the Persian armies, and other than being accredited for the concept of a Persian hoplite'esque troop type, the Cardaces, Xenophon in his written work "Horsemanship", does not only recommend the parameridia, but also lauds an invention called "The arm", a very possible and likely addition of laminated armour, or as they are called in Greek, the "cheires". It is often suggested that Seleucid heavy cavalry came to adopt the banded/laminated armour for the arms from the Achaemenians. However, before the demise of the Achaemenians, a third reform was made during the reign of Darius III Codomannus, after the battle of Issus. Modelled after previous Achaemenid as well as Bactrian style armour, and combined Sakae and Macedonian cavalry tactics, the Hûvakâ of Darius was an interesting, but nonetheless fearsome amalgam. By the end of the Achaemenid dynasty, the Persians had two types of shock cavalry, the most popular undoubtly the scythed chariot often pulled by armoured horses and lead by heavily armoured crew. The second being an exotic variety of extra-heavy cavalry, household but also recruited from the Bactrians, Massagetae, Sakae, Cappadocians, Armenians and even westernly Scythians. The interesting aspect is that instead of completely relying on local traditions, the Achaemenians pursued their own reforms of the heavy cavalry. While for most of its lifespan being more of a extra-heavily armoured skirmisher cavalry with the ability to mount a charge in column formation, it evolved into a unit meant for full contact. It was aptly named the "Hûvakâ", meaning "The Kinsmen", something translated by Pahlavî as "xwesawand" or "Khûveshâvagân".
Naturally this would also require not only great physique and vigour of the mountee, but the requirements of the mount would be more strict as well. A horse, able to support a heavily armoured rider and some barding needed to be heavy-boned, tall, and muscular. Historically, by the end of the Achaemenian era, Persian emperors were given tribute, often in the form of horses. Cyrus The Great himself valued horses besides good weapons and chariots, as quoted from Herodotus. The main breeds for heavier cavalry were the Cappadocians, as earlier trained to serve as mounts for the famed Lydian lancers and subsequently the Perso-Hellenic kingdom of Pontus, as well as the Armenian horses known for their resilience, and finally the Mede and Parthian (Nisaean) breeds, in which especially the latter was not only known as perhaps the bulkiest of horses but also remarkably speedy, said to outrun the Iberian horses used by the Romans. Therefore it would seem that Achaemenian cavalry tradition formed the basis of subsequent Armenian and Pontic heavy cavalry, as well as providing the Seleucids with a vast range of not only heavy cavalry auxiliaries but also a variety of mounts. The Armenians and the Persian nobles of Pontus, being greatly influenced by Persian trends would most certainly have continued the tradition.
As a means of support for chariots, it could facilitate the sheer violence of the chariot charge as written by Xenophon: "The soldiers had got into the habit of collecting their supplies carelessly and without taking precautions. And there was one occasion when Pharnabazus, with 2 scythed chariots and about 400 cavalry, came on them when they were scattered all over the plain. When the Greeks saw him bearing down on them, they ran to join up with each other, about 700 altogether; but Pharnabazus did not waste time. Putting the chariots in front, and following behind them himself with the cavalry, he ordered a charge. The chariots dashing into the Greek ranks, broke up their close formation, and the cavalry soon cut down about a hundred men. The rest fled and took refuge with Agesilaus, who happened to be close at hand with the hoplites." (Xenophon Hellenica IV,1,17-19)