The offices of satrap, or civil administrator, and commandant, or commander of the troops, were vested in the same person, who came in this way to have that full and complete authority which is possessed by Turkish pashas and modern Persian khans or beys--an authority practically uncontrolled.

This system was advantageous for the defence of a province against foes; but it was dangerous to the stability of the Empire, since it led naturally to the occurrence of formidable rebellions.
Two minor points in the scheme of Darius remain to be noticed, before this account of his governmental system can be regarded as complete.
These are his institution of posts, and his coinage of money.
In Darius's idea of government was included rapidity of communication.
Regarding it as of the utmost importance that the orders of the Court should be speedily transmitted to the provincial governors, and that their reports and those of the royal secretaries should be received without needless delay, he established along the lines of routes already existing between the chief cities of the Empire a number of post-houses, placed at regular intervals, according to the estimated capacity of a horse to gallop at his best speed without stopping.

At each post-house were maintained, at the cost of the state, a number of couriers and several relays of horses.

When a despatch was to be forwarded it was taken to the first post-house along the route, where a courier received it, and immediately mounting on horseback galloped with it to the next station.

Here it was delivered to a new courier, who, mounted on a fresh horse, took it the next stage on its journey; and thus it passed from hand to hand till it reached its destination.