Geographic and environmental attributes of a given region assume a pivotal role in the formation and persistence of human settlements. Nature confers possibilities and resources on human, who, as per his understanding of them, employs them in pursuit of his goals, hence the rise of human–nature interaction. The frequency of and the ways in which human settlements are established and the type of functions they serve with regard to environmental characteristics give rise to the ecology, which aims to grasp the scope of the interrelationships between humans and the environment. The present paper examines the scope of human-environment interactions in the Parthian period over the geographic extent of ​​the central part of the Kopeh dagh-Aladagh corridor.
The paper seeks to ascertain the local environment’s influence on the formation and evolution of Parthian settlements and to find out the pertinent settlement patterns in northern Khorasan.
Given the environmental potentialities, what were the Parthians’ criteria for site location when establishing their settlements? How did these priorities affect the distribution of sites and their settlement pattern in the study area?  The present paper represents a multifaceted research drawing upon archaeological survey, ecological studies, information processing in GIS, examining the relationships between natural and cultural variables and their impact on the formation of the contemporaneous settlements, and finally archaeological analysis.  The study adopts an ecological and economical approach. In this context, ecological data on the relation between soil type, geology, flora, fauna, and water table or “biosorption analysis” have been used. Processual archaeologists use ecological systems as their basic model for observing the adaptive transformations humans in response to environmental circumstances as even small environmental alterations will have the potential to affect cultural structures.
The Kopeh dagh-Aladagh corridor stretches from Garmab in western North Khorasan to the Mashhad plain to the east. For the purposes of this study, the corridor is divided into the following three separate parts based on geographic features that someway affect cultural aspects: a) Western part: extending from the beginning of the village of Garmab to the border of Shirvan County (Reza Abad), this part is characterized by a mountainous terrain with narrow passes such as Badranlu; b) Central part: in this part, defined by the beginning of Shirvan County (Reza Abad) and the end of Quchan County, the plains grow wider as the mountains begin to sit back; c) Eastern part: Chenaran County and the Mashhad plain mark the extreme boundaries of this part. The focus of the present work is on the central corridor, viz. the stretch delineated by the counties of Shirvan, Farooj and Quchan (Figure: 1). Geographically, the study area encompasses the structural valley of Atrak-Kashafrud, an expanse that is bounded by the mountains of Kopeh Dagh/Hezar Masjed to the north and the Aladagh/Binalud mountains to the south (Figure:2). This plain geomorphological unit exhibits a fairly wide and flat landform, and is principally affected by the sedimentary process of the flowing water bodies of the Kashafrud and Atrak rivers and their tributaries. Geomorphology, it consists of three main units of plain, foothills, and mountains. Its northern and southern sectors are mountainous, its slopes are characterized by foothills, and its central part consists of plain. Indeed, the mountainous quarters comprise small, narrow intermontane plains, which fall in the plain sub-class. The regional heights follow the northwest-southeast trend dictated by the general orientation of the Kopeh dagh zone. The Atrak and Kashafrud rivers rise from the regional mountains, forming two drainage basins. The archeological survey of the concerned area recorded more than 500 archaeological mounds and sites spanning the Chalcolithic to the Islamic period. Based on a comparative analysis of the surface pottery, 20 Parthian sites are distinguishable. It is notable that due to the lack of adequate knowledge of common Parthian pottery forms in the region, due caution has been exercised in the identification of these sites. These Parthian sites are divided between 16 examples lying in the northern half of the plain on the southern slopes of Kopeh dagh/Hezar Masjed and 4 instances that occur in the southern half on the northern slopes of Aladagh. As stated, a main objective of this study is to pin down the influential factors of the region's ecology in the formation of Parthian sites and their distribution in the geographic setting of the central Kopeh dagh-Aladagh corridor. To this end, such components as geology, altitude, slope gradient and aspect, climate, water resources and soil are explored. Finally, the results of the study reveal a close and direct correlation between the site location and the environmental factors (Figures: 3-10). The central Kopeh dagh/Hezar Masjed corridor on the north and Aladagh/Binalud on the south form an upland district hemmed in by mountains. Due to its mountain geomorphology, the area is generally dominated by cold, dry climate. In mountainous regions, slopes and valleys generally offer more advantageous conditions for settlement as the altitude variable prompts reduced temperature and increased humidity. Dropped temperature in warm seasons results in lowered evaporation of water resources, making water resources more easily accessible throughout the year. The choice of appropriate altitude as an influential factor in human activities has thus led to the concentration of Parthian settlements on the slopes dominating the plain. Choosing slopes provided the local populations with access to montane pastures, but also enabled them to exploit alluvial and fertile plains. The same strategy is still operative in the region, where, save for the cities that lie in the plain, rural settlements mostly sit on the slopes overlooking the plain. The distribution of the sites in reference to the slope gradient and aspect shows that, with the exception of F 0026, the Parthian sites lie in proper points of terrain ruggedness and slope gradient spectra, and their dominant slope aspect indicates the maximum use of solar heat in this cold region, with advantageous impacts on agricultural production and pastures. Given their location on slopes, the hitherto identified Parthian sites mostly occur on the spring-fed influent streams that flow into the Atrak, with no instances recognized along the latter. In light of the results from environmental studies, the altitude, slope gradient, easy access to water resources, and fertile soil served as the foremost factors governing the distribution of Parthian sites in the region as they were directly linked with subsistence. It is notable that while our environmental studies drew on the present-day landscape, the survey of the study area produced about 500 sites dating between the Chalcolithic to the Islamic period, and presence of this huge number of sites over this protracted timespan testifies to the fact that advantageous environmental conditions did prevail in the past.