Uniformity, or a near approach to it, was produced, not so much by the abolition of differences as by superadding one and the same governmental machinery in all parts of the Empire.  It is an essential feature of the satrapial system that it does not aim at destroying differences, or assimilating to one type the various races and countries over which it is extended.  On the contrary, it allows, and indeed encourages, the several nations to retain their languages, habits, manners, religion, laws, and modes of local government.  Only it takes care to place above all these things a paramount state authority, which is one and the same everywhere, whereon the unity of the kingdom is dependent.  The authority instituted by Darius was that of his satraps.  He divided the whole empire into a number of separate governments—­a number which must have varied at different times, but which seems never to have fallen short of twenty.  Over each government he placed a satrap, or supreme civil governor, charged with the collection and transmission of the revenue, the administration of justice, the maintenance of order, and the general supervision of the territory.  These satraps were nominated by the king at his pleasure from any class of his subjects, and held office for no definite term, but simply until recalled, being liable to deprivation or death at any moment, without other formality than the presentation of the royal firman.  While, however, they remained in office they were despotic—­they represented the Great King, and were clothed with a portion of his majesty—­they had palaces, Courts, body-guards, parks or “paradises,” vast trains of eunuchs and attendants, well-filled, seraglios.  They wielded the power of life and death.  They assessed the tribute on the several towns and villages within their jurisdiction at their pleasure, and appointed deputies—­called sometimes, like themselves, satraps—­over cities or districts within their province, whose office was regarded as one of great dignity.  They exacted from the provincials, for their own support and that of their Court, over and above the tribute due to the crown, whatever sum they regarded them as capable of furnishing.  Favors, and even justice, had to be purchased from them by gifts.  They were sometimes guilty of gross outrages on the persons and honor of their subjects.  Nothing restrained their tyranny but such sense of right as they might happen to possess, and the fear of removal or execution if the voice of complaint reached the monarch.

Besides this uniform civil administration, the Empire was pervaded throughout by one and the same military system.  The services of the subject nations as soldiers were, as a general rule, declined, unless upon rare and exceptional cases.  Order was maintained by large and numerous garrisons of foreign troops—­Persians and Medes—­quartered on the inhabitants, who had little sympathy with those among whom they lived, and would be sure to repress sternly any outbreak.