The Parthians were essentially a warlike people; and the chief interest which attaches to them is connected with their military vigor and ability. It is worth while to consider at some length the peculiarities of that military system which proved itself superior to the organization of the Macedonians, and able to maintain for nearly three hundred years a doubtful contest with the otherwise irresistible Romans.
We are told that the Parthians had no standing army. When war was proclaimed and the monarch needed a force, he made his immediate vassals acquainted with the fact, and requested each of them to marshal their troops, and bring them to a fixed rendezvous by a certain day. The troops thus summoned were of two kinds, Parthian and foreign. The governors of the provinces, whether tributary kings or satraps, called out the military strength of their respective districts, saw to their arming and provisioning, and, marching each at the head of his contingent, brought a foreign auxiliary force to the assistance of the Great King. But the back-bone of the army, its main strength, the portion on which alone much reliance was placed, consisted of Parthians. Each Parthian noble was bound to call out his slaves and his retainers, to arm and equip them at his own expense, and bring them to the rendezvous by the time named. The number of troops furnished by each noble varied according to his position and his means; we bear in one instance of their amounting to as many as 10,000, while in another recorded case the average number which each furnished was no more than 125. The various contingents had their own baggage-trains, consisting ordinarily of camels, in the proportion (as it would seem) of one to every ten fighting-men.
A Parthian army consisted usually of both horse and foot, but in proportions unusual elsewhere. The foot soldiers were comparatively few in number, and were regarded as of small account. Every effort was made to increase the amount and improve the equipment of the horsemen, who bore the brunt of every fight, and from whose exertions alone victory was hoped. Sometimes armies consisted of horsemen only, or rather of horsemen followed by a baggage train composed of camels and chariots.