Note 436 — Chapter VIII · CONNEXION BETWEEN THE ROMAN LAND SYSTEM AND THE LATER MANORIAL SYSTEM.
Reading edition
From angarius = ἄγγαρος, a messenger or courier. The word is probably of Persian origin.
'Nothing mortal travels so fast as these Persian messengers. The entire plan is a Persian invention. . . . The Persians give the riding post the name of "angarum."'—Herodotus, bk. viii. 98.
See also the Cyropædia, bk. viii. c. 17, where the origin of the post-horse system is ascribed to Cyrus.