The purpose of the article is to prove the presence of a deep (archaic) ideological foundation in the Roman-Persian political and legal complementarity of the times of late antiquity. Methods. The author uses the «panoramic approach», сomparative analysis of primary historical sources and the structural-functional method. Results. The author’s attention is devoted to the antique community in the legal content of imperial titles, the correlation of temporary and spatial understanding of the power of the Roman emperors and the power of the Persian Šâhanšâh’s. The main author’s thesis: 1) the provision on the Hellenization of Persia during the time of Khosrow Anushirvan; 2) the thesis on the principle of extraterritoriality of imperial power, formulated by the Romans in the era of dominatus and transfered from the Eastern Roman Empire into the Sassanian Eranshahr; 3) the author’s definition of the imperial form of government, based on the principle of «over-sovereignty» common to Iran and Byzantium. Discussion. Firstly, the spaces of Eranshahr and the Roman Empire were considered by ancient intellectuals as the «common heritage» of the Hellenistic Asian kingdom of Alexander the Great. Secondly, the roots and semantic content of the titles of the higher sovereigns of Persia and Rome (emperors) had common cultural and political origins and military-administrative premises. Thirdly, if at the initial stage of the interaction between the Persians and the Romans there was a strong influence of Persia on the everyday life of the population of the East Roman provinces, then in the 6th century the East Roman ethnocultural pattern «Christian Oecumene» became decisive in the Sassanian Mesopotamia.