Abstract
In recent decades, our knowledge about the Parthian period has increased significantly thanks to the valuable field researches mainly in the form of archaeological surveys. The target area of this research, Abbar and Darram districts, in Tarom Olia of Zanjan province, is also one of the areas where no information was available about its condition in the Parthian period. This research study 12 Parthian sites of the area, in order to answer questions such as the quality and quantity of settlements, The influence of climatic and environmental factors on the formation of sites, the characteristics of cultural materials and especially the typology of pottery, the differences and commonalities with the surrounding areas and the reconstruction of the historical and cultural image of the region in the Parthian period. The Parthian sites of the region were studied based on factors such as height, land slope, soil quality, and access to water sources and communication routes. Studying of Parthian potteries, including three groups of decorated, common and fillide, indicate that the pottery tradition of the region, in addition to having local characteristics, was influenced by the pottery traditions of the north, northwest and West of Iran, which indicates inter-regional connections and the role of Tarom region as a bridge between different parts of North-West Iran. The Parthian settlements were mainly formed near permanent water sources such as Ghezel-Ozan River and in low-slope, low-altitude and fertile lands. Due to the hydrological condition of the Tarom Valley and the abundance of water resources, all the Parthian sites access to sufficient water. According to the settlement pattern, it seems that the majority of the population of the area had a livelihood based on agriculture and gardening, in which the Darram Castle with an area of about 20 hectares played a key role in the area.
Keywords: Tarom Olia, Abbar, Darram, Archaeological Survey, Parthian Settlements.

Introduction
Zanjan province has long been one of the important areas for the formation of human sites in the northwestern part of Iran’s plateau due to its climatic conditions and geographical location as a communication corridor between the central plateau and the northwest of Iran. Tarom County, located in the northernmost part of Zanjan province, has the potential for the formation and relative development of human settlements. A season of archaeological survey in the area of Abbar and Darram in Upper Tarom County identified 12 Parthian sites based mainly on the typology of pottery, including Pavehrud, Dam, Foqlake 1, Foqlake 2, Emamzadeh, Vaznehsar, Darram, Oghlanqalasi, Govarqale 1, Govarqale 2, Govarqale 3, and Kuhkan Olya. This research, conducted through field and library studies, aims to investigate the Parthian sites in the region, exploring questions about the quantity and quality of Parthian sites, the influence of climatic and environmental factors on their formation, the typology of cultural materials (mainly pottery), and their differences and commonalities with surrounding areas. The Parthian pottery from the studied sites can be classified into three groups: decorated pottery, plain pottery, and Fillide pottery.

Environmental effects on formation of the Tarom Parthian sites
1. Water sources: In the Tarom region, along with the permanent flow of the Qezel-Uzan River, there are rich underground water sources, such as wells, canals, springs, tributaries, seasonal rivers, and channels, providing favorable conditions for the formation of human societies. In the studied area, nine sites are located less than 500 meters from rivers like Sherfan-Rud, Abbar, Nokian, Qeshlaq-Rud, and Vaznehsar, while two sites are situated less than 10 meters from Qezel-Uzan itself. Due to the hydrological conditions of the valley and the abundance of water sources, all sites in Abbar and Darram had access to sufficient water and were located near permanent water sources.
2. Hypsometry: The Parthian settlements in this area are located at different heights above sea level. Oghlanqalasi, at an altitude of 408 meters, and Dam, at an altitude of 1288 meters, are the lowest and highest Parthian sites in the study area, respectively. Overall, the Parthian sites in the region can be categorized into two groups based on altitude: those below 700 meters and those above 900 meters. There are 9 Parthian sites (75%) below 700 meters and only three sites (25%) above 900 meters. The first group is situated in valleys between mountains near rivers, while the second group is located on highland slopes.
3. Land slope: There appears to be a direct correlation between the elevation of Parthian sites in Abbar and Darram and the slope of the land. All nine Parthian sites in Abbar and Darram below 700 meters have slopes of less than 10 degrees, indicating that 75% of the sites are on low slopes and altitudes. Among the sites in Abbar and Darram, only 3 sites (25%) between 900 and 1300 meters have relatively steep slopes of 20 to 30 degrees. The slopes of the sites vary in direction, mainly north to south and west to east, highlighting the importance of sunlight in the formation of Parthian settlements in Abbar and Darram.
4. Land use: All Parthian sites below 700 meters with slopes less than 10% have fertile soil suitable for agriculture. The largest lowland and alluvial lands in the survey area are located on the northern edge of Qezel-Uzan, in the eastern and northwestern parts of Darram Castle. These lands have good access to water from the Siah Rud River to the north and the Ghezel Uzan River to the west.
5. Communication ways: Due to the topography of the area, communication routes have remained relatively unchanged over different periods, limited to inter-mountain valleys along rivers. The Parthian sites in this region are mainly aligned in a northwest-southeast direction along Qezel-Uzan or in valleys of sub-rivers perpendicular to the Qezel-Uzan River valley. The main modern communication road in the region follows a similar route along Qezl-Ozen. The proximity of Parthian sites to modern roads suggests that ancient roads likely followed a similar path.

Conclusion
In total, the sites located at an altitude of less than 700 meters, with an average size of 3.3 hectares, have good conditions for agricultural and horticultural activities due to easy access to water sources, good soil, and suitable slope. Additionally, sites located at a height of more than 900 meters above sea level, with an average area of 0.79 hectares, are situated in the middle of valleys and on sloping surfaces near tributary rivers, with rich pastures and water resources, making them favorable for animal husbandry activities. Moreover, the size and density of Parthian sites in the lower areas are much greater than in the higher areas. Considering that the size and density of the sites indicate the population living in the region, it appears from the results of our study that the dominant population of Abbar and Darram in the Parthian period had a subsistence economy based on agriculture and horticulture.
Among the identified Parthian sites, the site of Darram Castle, with an area of about 20 hectares, is a massive fortification structure on the northern bank of Qezel-Uzan. Given some features of Darram Castle such as its large size, fortification, easy access to permanent water sources, and access to agricultural land, it seems that Darram Castle played a key role throughout the study region in the last centuries of the Parthian period. The results of the study indicate that the pottery tradition in the region, in addition to being influenced by internal and local factors, was influenced by neighboring regions in the north, northwest, and west of Iran.