Angaria (Latin; Greek: αγγαρεία, angareía) was a sort of postal system adopted by the Roman imperial government from the ancient Persians. According to Xenophon, the Persian system 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 dispatches by night and day in all weather. The Roman system took its name from the Greek form of a Babylonian word adopted in Persian for these mounted couriers. In the Roman system, the supply of horses and their maintenance was a compulsory duty from which the emperor alone could grant exemption.