Abstract Considering special geographical location of Dargaz Plain in Razavi Khorasan province, identifying the cultural evolution there during the Parthian period can answer many questions about this relatively unknown historical era of Iran. Besides, it can help us better understand the origin of the Parthian culture in Northeast Iran. This research was carried out in the form of a reconsideration project during the field studies of Dargaz Plain. In this regard, Dargaz Plain was surveyed during one season, and as a result, 84 sites belonging to the Parthian period were identified. The main purpose of the research was tfo study the distribution patterns of Parthian settlements and their spatial relations with each other based on environmental variables. The most important environmental indicators in explaining the settlement patterns were analyzed via attributes such as altitude, water resources, slope, communication routes, vegetation, and land use, as well as the characteristics of the sites, including size and chronology using the geographic information system (GIS) and the cluster analysis method. The results indicate that during the Parthian period, the area witnessed an increasing growth in the nomadic population compared to permanent settlements, and in general three settlement patterns were identified: small and large villages, an urban center, and nomadic and seasonal settlements. Keywords: Parthian
