Here's an excerpt from Herodotus, Book 8, section 98. Xerxes, the Great King of Persia has just been beaten at the Battle of Salamis and wants to call home...
"...Xerxes dispatched a courier to Persia with the news of his defeat. No mortal thing travels faster than these Persian couriers. The whole idea is a Persian invention, and works like this: riders are stationed along the road, equal in number to the number of days the journey takes - a man and a horse for each day. Nothing stops these couriers from covering their allotted stage in the quickest possible time - neither snow, rain, heat, nor darkness. The first, at the end of his stage, passes his dispatch to the second, the second to the third, and so on down the line, as in the Greek torch race which is held in honour of Hephaestus. The Persian word for this form of post is aggareion."
Which today we would translate as the King's Messengers. The Great Kings used this system to manage their empire, the largest the world had yet seen. A road system maintained at state expense ensured the couriers could get from one end of the empire to the other very quickly, the most famous route being the Royal Road, which stretched from the capital Susa, in what is now Iran, to Ephesus on the west coast of what is now Turkey. (Actually the Royal Road stopped at Sardis, but Ephesus was only a short extra hop).
If you think of the road system as the backbone, the King's Messengers as the network transport layer, the dispatches as data packets, and the staging posts as routers, then the Persian system is like a very early, very manual version of the internet.
US readers might have noticed something familiar in the quote from Herodotus. The unofficial motto of the US Postal Service is Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds. Compare it to: Nothing stops these couriers from covering their allotted stage in the quickest possible time - neither snow, rain, heat, nor darkness.
That's right. The US postal creed comes direct from this verse of Herodotus.