Investigation and analysis of the role and position of the city of Theodosiusopolis in the relations between Iran and Byzantium in the Sassanid era

Abstract Armenia is among the Caucasian territories and has caused tensions between Iran and the Byzantine since its capture by the Parthians until the end of the Sassanid period. The continual fighting of the two ancient powers over the country made it a division in the year 387. After this division, Theodosius the First ordered that the border town of Theodosipolis be created in the western part of Armenia. The city was built on a hillside in the Karin area near the sources of the Euphrates River. The results of this study indicate that the Byzantines sought to build some solid fences in the border towns, including Teodosipolis, and the establishment of sufficient forces there, in order to prevent the rapid advance of the Iranian army in the Byzantine territory and could even In some cases, those cities would invade the Sassanian lands. The Sassanians, with the capture of the city, could have more easily attacked the eastern lands of the Byzantine Empire; besides, the occasional seizure by Iranians of the city caused the Byzantines not to fight their forces To organize the lands of Iran, and to focus more on the reconstruction of this castle-town, which had the shield for the Byzantine Empire. The existence and strengthening of fortresses in this city, which had a specific geographic location and strategy, indicated that the capture of this city was dominated by the possession of the Caucasus, Asia Minor, Mesopotamia and Syria, and was lost. Giving the city a major shift in the balance of power between the two empires.Keywords: Armenia, Sassanid Empire, Byzantine Empire, Theodosipolis Armenia is among the Caucasian territories and has caused tensions between Iran and the Byzantine since its capture by the Parthians until the end of the Sassanid period. The continual fighting of the two ancient powers over the country made it a division in the year 387.