Angaria (from ἄγγαρος, the Greek form of a Babylonian word adopted in Persian for "mounted courier"), a sort of postal system adopted by the Roman imperial government from the ancient Persians, among whom, according to Xenophon (Cyrop. VIII. 6; cf. Herodotus VIII. 98) it was established by Darius the Great. Couriers on horseback were posted at certain stages along the chief roads of the empire, for the transmission of royal despatches by night and day in all weathers. In the Roman system the supply of horses and their maintenance was a compulsory duty from which the emperor alone could grant exemption. The word, which in the 4th century was used for the heavy transport vehicles of the cursus publicus, and also for the animals by which they were drawn, came to mean generally "compulsory service." So angaria, angariare, in medieval Latin, and the rare English derivatives "angariate," "angariation," came to mean any service which was forcibly or unjustly demanded, and oppression in general. In modern Greek the word "αγγαρεία" came to mean as well a service or task only grudgingly undertaken by the one forced to perform it.