Because messages could be transmitted without delay and without waiting for riders to rest, the system provided unprecedented communication speed, which was not surpassed in the Middle East until the introduction of the telegraph.
In order to rule and maintain cohesion within the empire, the king, his court officials and his governors in the provinces needed a fast and reliable system to communicate.
Their infertility and need of extensive training meant that they were expensive, but their strength, hardiness and low maintenance made them ideal for long-distance travel in the conditions and climates of the Neo-Assyrian Empire.
Riders in the Assyrian communication system typically travelled with two mules, so that they did not become stranded if one became lame, and to alternate mounts in order to keep them fresh.
[6] Rather than relying on a trusted envoy to travel the entire distance, in the relay system each individual rider covered only a segment of the route.
Sometimes both methods were used simultaneously, such as in the case of a surviving letter from then-crown prince Sennacherib to his father Sargon II.
[9] To support the communication system, governors of the empire maintained a series of stations in their provinces at regular intervals along the king's road.
[10] However, unlike the caravanserais, the Assyrian road stations were for the exclusive use of authorized state messages and not open to private travelers.
Professor of ancient near-eastern history Karen Radner estimated that it was available to a group of about 150 officials who were called the "Great Ones" of Assyria.
[8] Radner estimated that a message from the western border province of Quwê (near modern-day Adana, Turkey) to the Assyrian heartland – 700 kilometres (430 mi) as the crow files and requiring the crossing the Euphrates, the Tigris and many tributaries, none of which had bridges – took less than five days to arrive.
[18] The use of relays of anonymous messengers – instead of a trusted envoy who must travel the entire distance – was a practice that the Assyrians introduced and remains the basis of today's postal systems.