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.