Encyclopædia Britannica, Ninth Edition/Angaria

ANGARIA (ἀγγαρεία), a sort of government postal system adopted by the Romans under the empire, borrowed from the ancient Persians, among whom, according to Xenophon, it was established by Cyrus. Couriers (angari, ἄγγαροι) on horseback were posted (positi), at certain stages along the chief roads of the empire, for the transmission of royal despatches by night and day in all weathers. The supply of horses and their maintenance were compulsory, constituting under the Romans a burden from which the emperor alone could grant exemption. Hence the word came to mean generally compulsory service in the despatch of royal messages.