Studying the Population Increase of Central Zagros During the Chalcolithic Period: Case Study of Archaeological Survey of Nahavand, Asad Abad, Kangavar, Sahneh and Harsin plain

In Archaeological Studies of the Fertile Crescent, the Central Zagros region is very important, due to its special geographical and geomorphological features, mountains and plains between the mountains and creates the appropriate environment for the formation of the settlement in various eras. The most important indicators of cultural changes in the Chalcolithic period are human-environment interaction, population growth, expansion of cultural exchanges, more specialized jobs, technology development Tooling, familiarity with the metals and metallurgy, focus on rural and food production. The needed information research is obtained through the archaeological survey; statistic data of the research are obtained of five regions of Asadabad, Skinheads, Kangavar, Sahneh and Harsin. Here, by survey the 152 Chalcolithic sites in the region, we are trying to investigate the settlements and population increase phenomenon on the basis of newly discovered evidences; as there is increasing number of settlements during the early to late Chalcolithic period. Overall, the analysis shows that most of data is about the sites related to late Chalcolithic period and Maximum area and average altitude in the whole areas as well and the next group with largest number and area is sites attributed to Middle Chalcolithic. This evidence suggests that during the early to Late Chalcolithic period settlements needed more lands to settle, so they move to the highlands. But it also requires appropriate conditions for living in highlands as these areas have all the necessary parameters for population growth; this conditions to increase the extent of the settlements and population would provide by rising trend of altitude and also sites close to rivers during the early to late Chalcolithic and it seems that in this region over-population is a widespread phenomenon. As the matter of fact, 89/57 percent of surveyed sites are located at an altitude of 1500 to 1800 meters above sea level (a.s.l) on the hilly area of piedmonts. This area is drained by several branches of the river; due to the relatively high slope areas has high-dens networks, both seasonal and casual. The sediments of surrounding mountains are heavey-densed due to the influence of seasonal networks around the slopes which resulted expanding the settlements and farms to down-stream slopes. In addition, about 62/5% of sites have located at a distance of less than 1000 meters from seasonal streams and networks. One of the common perceptions of people concentrations along the rivers would be mobility and nomadism; since the water supply needed temporarily for living along the rivers. Due to the high risk of being sedentary along the rivers, the sites must be locating in such condition which is away from the risk of flooding. Some evidence suggests that the nomadism started during chalcolithic period in Central Zagros for the first time. It certainly has been related to increasing settlements during the given period due to increasing of mobility or populations, changing conditions and looking for suitable places. On the other hand an increasing of chalcolithic settlements in the region, leading to different subsistence systems responding the population requirements. Looking at the data of this research about Kangavar valley (eastern Central Zagros) is evident that in the number of settlements there has been growth from the West to the East of the region during early to Late Chalcolithic period and this is probably due to the high pressure of population growth have moved towards western areas.