These 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 (c.484-c.420 BC) Greek historian
The Persian Wars, 8.98 [tr. Rawlinson (1942)]
Of the Persian messengers. The U.S. Postal Service adopted a variation on this motto: "Neither snow, nor rain, nor heat, nor gloom of night stays these couriers from the swift completion of their appointed rounds."