The horse were of two kinds, heavy and light. The heavy horsemen wore coats of mail, reaching to their knees, composed of rawhide covered with scales of iron or steel, very bright, and capable of resisting a strong blow. They had on their heads burnished helmets of Margian steel, whose glitter dazzled the spectator. Their legs seem not to have been greaved, but encased in a loose trouser, which hung about the ankles and embarrassed the feet, if by any chance the horseman was forced to dismount. They carried no shield, being sufficiently defended by their coats of mail. Their offensive arms were a long spear, which was of great strength and thickness, and a bow and arrows of unusual size. They likewise carried in their girdle a short sword or knife, which might be used in close combat. Their horses were, like themselves, protected by a defence of scale armor, which was either of steel or bronze. The light horse was armed with the same sort of bows and arrows as the heavy, but carried no spear and wore no armor. It was carefully trained to the management of the horse and the bow, and was unequalled in the rapidity and dexterity of its movements. The archer delivered his arrows with as much precision and force in retreat as in advance, and was almost more feared when he retired than when he charged his foe. Besides his arrows, the light horseman seems to have carried a sword, and he no doubt wore also the customary knife in his belt. We are told by one writer that it was a practice of the Parthians to bring into battle a number of led horses, and that the riders from time to time exchanged their tired steeds for fresh ones, thus obtaining a great advantage over enemies who had no such practice. But the accounts which we have of Parthian engagements make no reference to this usage, which we can therefore scarcely suppose to have been adopted to any large extent. It may be doubted, also, if the practice could ever be one of much value, since the difficulty of managing led horses amid the tumult of a battle would probably more than counterbalance the advantage derivable from relays of fresh steeds. During the later period of the monarchy, the Parthians, who had always employed camels largely in the conveyance of stores and baggage, are said to have introduced a camel corps into the army itself, and to have derived considerable advantage from the new arm. The camels could bear the weight of the mailed warrior and of their own armor better than horses, and their riders were at once more safe in their elevated position and more capable of dealing effective blows upon the enemy. As a set-off, however, against those advantages, the spongy feet of the camel were found to be more readily injured by the _tribulus_, or caltrop, than the harder feet of the horse, and the corps was thus more easily disabled than an equal force of cavalry, if it could be tempted to pass over ground on which caltrops had been previously scattered.