It is said that as many days as there are in the whole journey, so many are the men and horses that stand along the road, each horse and man at the interval of a days journey; and these are stayed neither by snow nor rain nor heat nor darkness from accomplishing their appointed course with all speed.
HerodotusThese 'messengers' will not be hindered from accomplishing at their best speed the distance which they have to go, either by snow, or rain, or heat, or by the darkness of night.
Herodotus