Abstract
The investigation and study of the plains and valleys between the mountains of South Zagros in Iran from a geographical and cultural point of view leads to a deeper understanding of how the archaeological cultures of those regions were formed and expanded; The southern parts of Zagros have their own geographical and cultural areas, while the northern regions include Abadeh, Eghlid, and Semirom; The Ghabr-e Keykha river basins and Semirom region are significant for the study of cultural interactions and areas of expansion of the archaeological cultures of Fars province because of their location at the intersection of the archaeological cultures of South Zagros. Therefore, we started the studies to investigate the prehistoric settlements and demographic fluctuations of the Ghabr-e Keykha river basin and to identify the oldest habitation in the central part of Semirom. The current research was based on a season of the archaeological survey with a habitat analysis approach in the central part of Semirom city (Figure: 1); After preparing the required maps, we surveyed the target area, and random sampling was done. Due to the low environmental capabilities, the sites were not in the dimensions and size of settlements in the central parts of Fars. It has been considered from sources of water and quality soil and living in the closest distance to rivers and reliable sources of water; It is interesting to note that, unlike in the central parts of Fars, there is no evidence of a sharp decrease in the number of enclosures and a change in the lifestyle from a sedentary farmer to a nomadism, and we are witnessing the size of Sites and the increase in population during the Banesh period.
Keywords: Archaeological Survey, Prehistory, Semirom, North Fars, Southern Zagros.

Introduction
Semirom county has an area of about 5224 square kilometers and an average height of 2400 meters above sea level, and its location is in the south of Isfahan province on the slopes of the Zagros highlands. This county is in the middle of South Zagros and the eastern slope of Dena highlands. What turned Semirom County into a distinctive locale in the prehistoric and later periods was its obvious location at the interface of the three major Iranian cultural zones, namely Fars to the south, Bakhtiari to the west, and the central plateau to the north. Thus, the region represents a significant focal point for exploring the cultural interactions of the cited zones. What is evident with regard to the regional archaeological investigations is the lack of systematic surveys, local chronology, excavated sites, and knowledge of the cultural evolutions in prehistoric times.  From another geographical point of view, Semirom lay in the southernmost part of Isfahan, that is the lowermost focal point of the central plateau cultures, wherein the penetration of the Bakun culture cannot be ruled out.
The basic question concerns the circumstances of settlements and population fluctuations at the prehistoric sites in Central District of Semirom, focusing on the factors of settlement size, water resources and arable lands, in particular during the Bronze Age, to determine whether there are comparisons with the central parts of Fars? Another question is: Given the location of the Semirom region at the convergence point of the cultures of the central Fars, are there any evidences of cultural interactions with the latter cultures? Furthermore, since at the current status of our understanding, grounded in the excavations of Tall-e Mash Karim (Sardari and Taheri 2015, 266; Taheri 2015, 233), and Gol-Afshan (Taheri 2009, 345; Taheri, 2020), the region’s earliest occupations date to the Bakun period, we were looking for information about potential earlier Paleolithic and Neolithic settlements. Judging by previous surface surveys, albeit their partial coverage of the region, and excavations, I assumed that the region was under the influence of Fars archaeological cultures, and indications for influences from the Bakhtiari region and the central Iranian plateau are absent. Thus, testing this hypothesis called for carrying out more careful intensive surveys in parts of Semirom.

Discussion
From the Middle Paleolithic period, we identified three open sites, two of which were created on the terraces dominating the rivers, and one site with a long distance from the permanent water resources at the exit of one of the northern valleys of the region is surveyed. Earlier, the settlement in this area was dated to the Bakun period. But it dates back to the Middle Paleolithic period, according to new surveys and evidence of human activities identified from the Paleolithic period. From the Neolithic period, we identified only one site related to the Shams Abad period, but with the beginning of the Bakun period(Chalcolithic), like Fars, we see an increase in settlements from one Neolithic site to seven sites in the Bakun period and four sites in the Lapui period. Various causes can be involved in this increase in population. First, with the warming of the region after the late Holocene, in a way that was not much different from the current climate of the area (Sadat Hosseini et al., 2015), better conditions were provided for the expansion of settlements and human habitation. We can see its appearance at the beginning of the Shams Abad period and the identification of one site. On the other hand, with the revelation of the Bakun culture in the Kur river basin, which had progressed in the economic and social contexts, more possibilities and abilities were obtained to exploit the environment, such as the expansion of irrigation canals began in the Shams Abad era and reached its peak during this period. They used more diverse animals in their food chain through hunting and animal husbandry. Although, like Fars, we see an increase of sites in the Bakun and Lapui periods. it seems that the Semirom region should be introduced as one of the peripheral regions of Fars and influenced by the archaeological cultures of this region with its cultural characteristics, in terms of dimensions and number of sites, livelihood patterns, and pottery motifs. That needs to be studied separately and consider its specific climatic and geographical conditions in the framework of the archaeological cultures of Fars.
 In the Banesh period, the number of sites is reduced to three. It seems that this region, unlike Fars, in this period, not only has not a noticeable decrease in population compared to the Lapui period, but we can see the stability of the population and the size of the sites. Also, observing the beveled rim pottery (Figure: 7) in this region is an important issue that doubles the need for a more detailed study of the entire county in this period. 

Conclusion
The results indicated the influence of environmental factors in the selection of sites, and factors such as distance and proximity to reliable water resources, fertile lands with easier access to water, and a suitable slope were the main factors for choosing a place of habitation. In all prehistoric times, most of the sites were very close to the main branches of the rivers (Map: 3); Most of them have settled in the middle of the plain, where the ground is less steep and has better soil. The reason that we identified no areas in the foothills of the mountains and at a greater distance from the rivers is because of the factors such as more difficult access to water resources due to the greater depth of the valleys in the initial parts, the lack of good soil, and the impossibility of exploiting water resources through canalization. There may be other factors involved which require more research to identify. In this lifestyle, the location should be chosen more carefully because the stay duration was longer, and the soil and water resources use was continuous and planned. In the end, based on the model that most archaeologists use to estimate the population and their interpretations, i.e., determining 100 to 150 people for each hectare in prehistoric periods (Alizadeh, 1392: 159), we predicted a population of over 200 people for the central part of Semirom in the Neolithic period, considering that we identified only one site with an area of 15,000 square meters. After that, during the Bakun period, the total area of seven sites was 27,500 square meters, and the estimated population was about 550 people. In the Lapui period, the total area of all the sites was 18,000 square meters, with an estimated population of about 350 people. In the Banesh period, the total area of all the sites was 50,000 square meters, which reached around 1,000 people with the increase in population. This analysis clearly shows the beginning of the increase of the sites with the beginning of the Shams Abad period. It continues to increase in the Bakun period. In the Lapui period, we are facing a 40% decrease in the number of sites. Again, in the Banesh period, the size of the sites increased a lot, and we estimated the largest population for this period.