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Ahmadyousefi Sarhadi M, Montazer zohouri M, Amirhajloo S. (2025). The Role of Environmental Factors in the Distribution and Formation of Settlements in Rudbar Area in the Cultural Landscape of Halil Roud During the Islamic Era. Parseh J Archaeol Stud. 9(32), 187-218. doi:10.22034/PJAS.908
URL: http://journal.richt.ir/mbp/article-1-908-en.html

Abstract
South Rudbar Plain, with an area of more than 6000 square kilometers, is one of the important archaeological areas in the southeast of the Halil-Rood cultural area. This area, due to its favorable environmental conditions, including the permanent water of the Halil-Rood River, the fertile and vast plains, and the pasture heights in the northern part, as well as due to its geographical capacity and the communication route between Sindh and Sistan to Jiroft, was the foundation for the presence of human societies with the livelihood structures such as sedentary lifestyle and nomadic. As a result of two seasons of Archaeological surveys in South Rudbar plain during the last two decades, a number of ancient settlements were identified in this area. However, in these surveys, the focus is on pre-historic sites, while the sites of the Islamic era have not been studied deeply and completely, and only their GPS points have been recorded and incomplete descriptions of them have been provided. Therefore, answers have not yet been provided to questions about the role and influence of environmental factors on the distribution of Islamic settlements and the formation of livelihood organizations. In the following article, for the first time, the effect of environmental factors on Settlements of the Islamic era in Rudbar plain was studied with an analysis based on the findings of two archaeological surveys, documentary studies, and the preparation and interpretation of GIS maps. For this purpose, the settlements of Rudbar plain were divided into two time periods based on relative dating: “first to early middle Islamic centuries” and “late centuries (from the 10th century AH onwards)”. Then, environmental factors such as altitude above sea level, resources water, amount and direction of the slope of the lands, soil characteristics, and condition of roads in connection with settlement evidence were analyzed. The results of the research show that the most important factors affecting the formation, distribution, and organization of the livelihood of the Rudbar plain settlements in the Islamic era are the Halil-Rood River and the Aqueducts as the water sources in the peripheral parts, the trade route of Jiroft to Sind and Sistan, and the unevenness of the north and northeast for benefit from the potential of animal husbandry.
Keywords: South Roudbar, Environmental Factors, Distribution of Residence, GIS, Islamic Archaeology.

Introduction
The environment and its substrates are very important in examining the distribution pattern of ancient sites in a region. According to archaeological research, Rudbar plain has been a suitable place for human societies to live since at least the Copper Age (cf. Daneshi and Eskandari, 2016). This area as a commercial crossing (Yacoubi, 1963: 62) and one of the important areas of agricultural and livestock production (Sarhadi, 2017: 24), is very important in the archaeological studies of the Halil Road cultural area. However, the settlements of the Islamic era in the Rudbar plain do not have a share in the previous archeological studies and there are questions about this, which of the environmental factors and at what qualitative and quantitative level is effective in the distribution of settlements in the Rudbar plain in the south of Halil Roud cultural region during the Islamic era?
Based on this, the main purpose of this research is to investigate and analyze environmental factors affecting the formation and development of the Islamic settlements of Rudbar plain with a focus on geological features, altitude, water resources, and trade routes. Despite the numerous narratives of the early Islamic geographers about this region (see: Yaqoubi, 1963; Ibn Hawqal, 1966; Istakhari, 1994), no independent research has been done to identify and investigate the Islamic era settlements in Rudbar plain; and this issue shows the necessity and importance of this research. Also, the results of this research can help to understand the roots of the urban culture of this region in the early Islamic Middle Ages. 
The current research is historical research and a descriptive-analytical method was used. Research data has been collected by documentary and field methods. 

Discussion
The statistical database under study includes 53 sites and historical monuments, which are divided into two groups of settlement evidence, “first to seventh century AH” and “late Islamic centuries (Safavid and Qajar)” based on relative chronology (Tables 1 and 2). In order to explain the impact of environmental factors on the location of these sites and evidence, a geographic information system (GIS) has been used.

1. The effect of the height coefficient on the distribution of settlements
To explain the effect of height above sea level on the formation of the landscape and the distribution of the studied settlements, the height of the Rudbar plain is classified into eight classes (Figure 3, Chart 1). The largest number of cultural evidence representing the settlements of the Islamic era have been formed in this region at an altitude between 500 and 600 meters above the surface of open water, while only 4 sites have been found at an altitude of less than 400 meters above sea level. It seems that the large number of settlements at altitudes between 500 and 600 meters, which exactly covers the slopes of Rudbar Plain, is proof of the predominance of nomadic livelihoods in the Rudbar Plain during the Islamic era, and on the other hand, the small number of sites at an altitude of less than 400 meters can be analyzed in relation to the swampy condition of the Rudbar plain and the greater extent of the Jazmurian bed in the past.

2. The effect of water resources on the distribution of settlements
According to the maps obtained from GIS, most of the sites and evidence related to the settlements are located at a close distance from the surface water network, especially the Halil Rood River (Figure 4, Diagram 2). So, 17 sites, equivalent to 32% of the sites, were developed less than 5 kilometers away from Halil Rood River and under the direct influence of this water source. Another source of water is the Aqueduct. Among the sites of the Rudbar plain, especially those located on the edge of the plain and on the surface of the alluvial cone, were developed in connection with this water source (Figure 5).

3. The influence of the roads on the distribution of settlements
South Rudbar Plain was one of the important communication crossings of the Islamic era due to its location on the old communication and trade route from Indus to Jiroft (Yaqoubi, 1963: 62). According to the explanations of geographers about this ancient road, the current route of Rudbar to Iranshahr has been determined as a part of the aforementioned ancient route and the sites found have been investigated based on this route. As a result of this analysis, 17 sites with a significant linear extension in the west-east direction are located at a distance of 500 meters to 5 kilometers from this main communication road of the region (Figures 6 and 7, Diagram 3).

4. The influence of the slope of the land and its direction on the distribution of settlements
Based on the distribution map of sites and cultural materials related to the settlement of Islamic centuries in the Rudbar plain, we are facing a relatively flat land (Figure 8, Diagram 4). Regardless of the slope of the heights, we are facing a large and relatively flat plain where all the sites found were developed on a bed with a maximum slope of 5%. In fact, in terms of the relationship between the location of the sites and the slope of the land, no significant pattern can be defined. The settlements are located in various slope directions, including south, southeast, and southwest (Figure 9). Considering that the Rudbar plain is one of the tropical areas of the Halil River basin, it seems that the direction of the slope with a southern tendency is not logical. Therefore, it is clear that other environmental factors play a more important role in choosing a place of residence.

5. The effect of land use on the distribution of settlements
As a result of the land classification of Rudbar Plain based on the type of land use in the present era, four types of land use including pasture, agriculture, slopes, and the bed of Jazmurian Lake were investigated. Referring to the output map according to the type of land use, it seems that this factor played a decisive role in the distribution of settlements (Figure 10, Diagram 5). Considering the location of the settlements in connection with pasture and agricultural lands, the pattern of distribution can be interpreted in direct relation with the nomadic livelihood structure with a wider level and the agricultural structure with a smaller level during the Islamic era in the Rudbar Plain.

Conclusion
Rudbar plain is at the southern end of the Halil Rud cultural landscape and corresponds to the current city of Rudbar Jonoob. This region has been the foundation for the presence of human societies during the Islamic era due to its environmental talent, including the permanent water of the Halil River, fertile plains, and pasture heights, as well as being located on the ancient Sind-Jiroft trade route. Based on the analysis of settlement distribution and settlement evidence of the Islamic era and taking environmental factors into consideration, it seems that the cultural landscape of Rudbar plain during the Islamic era was mostly influenced by the variables of altitude, land use, and roads. As a result of the analysis, out of a total of 54 sites and settlement effects found, 50 points are affected by surface water sources such as Halil Rood River and aqueducts, as well as in connection with large pastures and small agricultural lands. Four other local evidence of settlement in the eastern end of the central plain, due to the lack of environmental facilities where they were formed, can only be explained in connection with the ancient road from Indus to Jiroft. Apart from these last four cases, the location of 13 sites/artifacts in the central plain of Rudbar, in addition to showing the relationship with other factors such as height and land use, has also been influenced by the road factor. In general, under the influence of the geographical and ecological factors of the Rudbar plain, the dominant livelihood of the people of the region during the Islamic era was formed based on providing resources through animal husbandry, agriculture, and trade.