Typology of Parthian and Sassanid Forts in Northern Khorasan and Determining the Position of the Region Based on its Cultural Interactions

Greater Khorasan, which is now divided into six countries, in addition to its geopolitical importance, have great historical importance due to the formation of the Parthian State and then the powerful presence of the Sassanid Empire along with the expansion of territory and protection of borders against the invasion of the Eastern nations. Despite these reasons, there is little information on past events in the area in the historical and archaeological sources. Iranian Khorasan occupies a large part of the northeast and east of the country. Archaeological survey in the middle part of the Kopeh Dagh-Ala Dagh corridor in northern Khorasan has identified various sites from the Parthian and Sassanid eras. Among the identified ancient sites, sixteen architectural structures were identified in the form of a fort. Recognizing the differences and similarities between the architecture of the forts with each other and then comparing them with other similar examples inside and outside the borders of Iran, led to a better understanding of the fort-building styles and their grouping in this region. In this research, in addition to identifying forts and recognizing their architectural features, using remote sensing, ecological studies and the type distribution of forts from each other. This article emphasizes the socio-political role of the study area as the last border access to the central plateau of Iran.