A dominion acquired by conquest can only be maintained by standing armies, and we cannot, therefore, be surprised to find the provinces of Persia constantly occupied by great masses of men, destined to keep them in subjection, as well as to defend them against a foreign invader. Immediately upon the completion of their conquests such forces were suffered to remain in the provinces, supported not by the king but by the conquered. Examples especially occur in the frontier states, in Asia Minor, Egypt, and others, which were especially exposed to assaults from without, or where an insurrection was most to be apprehended. Asia Minor, however, from the commencement of the wars with Greece, became the principal depot for the forces of Persia; it was filled with considerable bodies of men which could be readily drawn together when occasion required, and thus Alexander, on invading it, found there troops drawn together to oppose him on the banks of the Granicus.
In the most flourishing epoch of their history the military system of the Persians was as follows. In every province were kept up two descriptions of forces, those which occupied the open country, and those which kept possession of the cities, as garrisons. These were distinct, and commanded by different generals. Of the first description of forces it was clearly defined how many, and of what class, were to be maintained in each province. The principal strength consisted in cavalry, but there were also bowmen, slingers, and heavy-armed infantry. The care of keeping up the full numbers of these forces was committed to their successive commanders, and they were supported, both as respected food and money, by the revenues of the provinces, and as these were paid into the treasury of the satrap, the latter had to provide for the pay of the soldiery. The commanders, however, of the forces were not subject to the governors, unless by special appointment. On the other hand, they appear to have been immediately dependent on the king, having been appointed by him and deposed at his pleasure, and a catalogue of such offices remaining in his hands. The annual reviews of the forces also, which were extended to all the empire, were not usually held by the satraps, but in the neighbourhood of the capitals, by the king himself, and in remote provinces by persons deputed by him to hold them in his name. Great exactness was exercised on these occasions, and according to the good or bad condition of the forces their commanders were applauded and rewarded with presents, or deprived of their rank, or visited with arbitrary punishments.
To these arrangements was added another, the subdivision of the empire into certain military cantons, independent of the civil administration; formed with a reference to the muster-places of the troops. In this manner the forces stationed in a particular province were always collected at one point, from which the canton derived its appellation. Mention occurs of those in Asia Minor, and as the above institutions extended to the whole of the empire, and reviews were held in every province, it is to be supposed that this custom also was universal. Herodotus expressly mentions the cantons on this side the Halys, and consequently we must conclude the same to have prevailed on the other side. Of the cantons in Asia Minor, Xenophon particularises that of which the muster-place was the plain of Castolus, as that of Thymbra was for the army of Syria; Herodotus also mentions the Aleius Campus in Cilicia.
These troops were distributed through the provinces by thousands, and their commanders consequently denominated Chiliarchs; and not only were they generally dispersed over the country, but bodies of them were posted on the boundaries, where, if the nature of the ground permitted it, the passage from one province to another was strongly fortified. It certainly remains a question what was the strength of these forces in the provinces, but the great facility with which armies were got together proves them to have been very considerable. In Asia Minor alone Cyrus assembled above one hundred thousand men; Abrocomas, who was opposed to him on his march, had three hundred thousand; and the Persian army on the Granicus was forty thousand strong.
From these troops the garrisons in the cities were kept entirely distinct, and the importance attached by the Persians to places of strength was in proportion to the difficulty which (like all other nomad nations, who know nothing about the conduct of sieges) they had experienced in subduing them. They were looked upon as the keys of the provinces in which they were situated, and accordingly provided with ample garrisons. The troops in question were completely different from those mentioned above, not being comprehended in the military divisions alluded to, but being under commanders of their own, and not bound to appear at the general muster.
Both descriptions of forces were, however, comprehended under the title of the king’s army, and were distinct from the household troops of the satraps and grandees, which often amounted to several thousands. By the customs of the East every great man is attended by an armed retinue, proportioned to his rank and wealth, and as the viceregal courts were formed upon the model of the king’s, this became necessarily a part of their establishments, and the more readily as corps of troops were a no less customary present from the monarch to his favourites than were cities.
Originally, it is probable that all these troops may have been Persians, but as these gradually withdrew themselves from martial duties, their places were supplied by mercenaries, Greeks or Asiatics. As cavalry, the nomad nations to the south and east of the Caspian were preferred, the Hyrcanians, Parthians, and Sacæ. The first, especially, had a high character with the Persians for courage, and on this account the latter kept up a good understanding with the wandering hordes of Great Bucharia, though no longer their tributaries. The Greeks, however, were preferred to all the rest, and as early as the time of the younger Cyrus, not only did the flower of the army always consist of them, but towards the end of the Persian monarchy they constituted the garrisons of all the cities of Asia Minor. Before the time of the younger Cyrus their pay amounted to a daric per month (about 1l. 0s. 4d. sterling), which was augmented by Cyrus to a daric and a half. We have already remarked the fatal consequences which this custom had on the warlike temper of the Persians.
In a nation of conquerors every individual is expected to be a soldier, and among the Persians all, especially those in possession of lands, were required to be able to serve on horseback. This necessitated an internal constitution of the whole empire, having for its object the military equipment of the population; and the arrangement adopted has usually been the same in all Asiatic nations, and is the simplest that could have been devised. A decimal system runs through the whole empire, and serves at the same time to mark the rank of the commander. The common people are divided into bodies of ten, having a captain of that number, after whom come the commanders of hundreds, thousands, and tens of thousands. Officers of a higher rank are not apportioned to particular bodies of men, but form the general staff. This has been equally the case among the Mongols and the Persians, and this simple arrangement made it possible for both races to assemble large armies with incredible rapidity. All that was required was a mandate from the commander of ten thousand, which was transmitted to the commanders of thousands, and hundreds, and tens, till the forces, already organised, assembled in martial array. In this manner the Mongol princes often got together, in a few days, armies of cavalry to the number of several hundreds of thousands, and we cannot, therefore, be astonished to see the same thing take place among the Persians.