A chapter dealing with Iranian feudalism in a distinguished series dedicated to The rise and fall of the Roman world bears the title ‘Iran, Rome’s greatest enemy’. This title is more than merely a justification for the inclusion of a chapter on Iran in a work devoted to the history of the East Roman empire. It also reflects a host of fears and prejudices fostered for long centuries in the Roman world, since the trauma of Crassus’ defeat by the Parthians at Carrhae. Not even extended periods of decline and internal disarray within the Parthian monarchy, during which it was repeatedly invaded by the Roman army, could dispel the myth of the uncompromising threat posed by Iran to the Roman order. The replacement of the Parthian Arsacid dynasty by a vigorous new one, based in Fars, namely the Sasanian dynasty, at a time when the Roman empire itself was facing one of its severest crises, only aggravated its inhabitants’ deeply rooted fear of Iran. Ancient writers in the Roman oikoumenē passed on this attitude to modern western scholars.