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.  According to Xenophon, the messengers travelled by night as well as by day; and the conveyance was so rapid that some even compared it to the flight of birds.  Excellent inns or caravanserais were to be found at every station; bridges or ferries were established upon all the streams; guard-houses occurred here and there, and the whole route was kept secure from the brigands who infested the Empire.  Ordinary travellers were glad to pursue so convenient a line of march; it does not appear, however, that they could obtain the use of post-horses even when the government was in no need of them.  The coinage of Darius consisted, it is probable, both of a gold and silver issue.  It is not perhaps altogether certain that he was the first king of Persia who coined money; but, if the term “daric” is really derived from his name, that alone would be a strong argument in favor of his claim to priority.  In any case, it is indisputable that he was the first Persian king who coined on a large scale, and it is further certain that his gold coinage was regarded in later times as of peculiar value on account of its purity.  His gold darics appear to have contained, on an average, not quite 124 grains of pure metal, which would make their value about twenty two shillings of our money.  They were of the type usual at the time both in Lydia and in Greece—­flattened lumps of metal, very thick in comparison with the size of their surface, irregular, and rudely stamped.  The silver darics were similar in general character, but exceeded the gold in size.  Their weight was from 224 to 230 grains, and they would thus have been worth not quite three shillings of our money.  It does not appear that any other kinds of coins besides these were ever issued from the Persian mint.  They must, therefore, it would seem, have satisfied the commercial needs of the people.