Quote Originally Posted by Tellos Athenaios
Some ancient 'yardstick': Sardis - Sousa : ~3 months' journey.
An elaboration on this; For couriers on duty per "parâsang" (Per unequal hour) this distance could be reduced to a handful of days if the Royal Road was used, and especially if caravansaries entered the picture. The Sassanians optimized this system of intelligence by increasing the figure of out-posts, to such degree that in application it became a human "telephone"-line (News were literally shouted); Under ideal circumstances news would reach the court in Ctesiphon by mere hours.

It is bedazzling indeed how infantry armies with convoluted logistics and heavy baggage covers this distance, in contrasts to an equestrian army with minimal baggage.