Persian couriers

Persian couriers were ancient mounted messengers (despatch riders) kept ready at regular stages throughout old Persia for carrying the royal despatches at the time of the Achaemenid Empire.
Terminology.
In Ancient Greek, Persian courier was called "ἄγγαρος" (ángaros, “Persian mounted courier”), whence Latin "angarius", which is probably from an East Asian language (e.g., Sanskrit "अजिरा" (ajirā, “agile, swift”)). The word "angel" ("ἄγγελος") is probably loaned from and related to Greek "ἄγγαρος".
History.
In about 440 BC, Herodotus wrote in "The Histories" (book 8.98) about the Persian couriers:
Paraphrase of the Herodotus description was used by the United States Postal Service as a motto on the entrance to the Central Post Office building in New York City: "Neither snow, nor rain, nor heat, nor gloom of night stays these couriers from the swift completion of their appointed rounds."