"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 route 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. "_Note._--It was not the distance a horse ridden gently could accomplish in the entire day, but the distance he could bear to be galloped once a day. From the account which Herodotus gives of the post-route between Sardis and Susa, we may gather that the Persians fixed this distance at about fourteen miles."--George Rawlinson, _The Five Great Monarchies of the Ancient Eastern World_, London, 1871, vol. iii. pp. 426-7. _Roman Empire._ "The advantage of receiving the earliest intelligence, and of conveying their orders with celerity, induced the Emperors to establish throughout their extensive dominions the regular institution of posts. Houses were everywhere erected at the distance only of five or six miles; each of them was constantly provided with forty horses, and, by the help of these relays, it was easy to travel an hundred miles in a day along the Roman roads. The use of the posts was allowed to those who claimed it by an Imperial mandate; but though originally intended for the public service, it was sometimes indulged to the business or conveniency of private citizens (Pliny, though a favourite and a minister, made an apology for granting post-horses to his wife on the most urgent business)."--Edward Gibbon, _The History of the Decline and Fall of the Roman Empire_, London, ed. 1896, vol. i. p. 50. _Arabia._