Abstract
Most of our knowledge on the Palaeolithic of the Iranian Plateau derives from a scientific focus on the area of the Zagros Mountains. In recent years, several Palaeolithic research projects have been conducted in different parts of Iran, including southern piedmonts of the Alborz Mountains and the Iranian Central Plateau. The present paper is an introduction to the archaeological pieces of evidence of a Palaeolithic occupation on the southern slopes of the Alborz Mountains. Sorheh Rockshelter is the first site among a cluster of 8 caves and rock shelters located around 80 km northwest of Tehran. The Palaeolithic artifacts have been recovered from at least three looters’ pits at the center of the rock shelter. Sorheh is significant at least for two aspects: firstly, since the southern slopes of the Alborz Mountains have not yet been identified for the Palaeolithic, the site provides unique data on the Iranian Plateau. Secondly, the site’s location and the physiogeographic and lithic analyses of Sorheh are invaluable for the reconstruction of hominin behavior and settlement patterns in this under-researched area. 
Keywords: Central Iranian Plateau, Alborz Mountains, West-Central Zagros, Middle Palaeolithic, Levallois.

Introduction
Compared to the wealth of Palaeolithic data from the Zagros region, the piedmonts of the Alborz Mountains have received little scientific attention. The focus has been on the northern slopes, although the intermountain valleys of the southern Alborz Mountains could have been biogeographically suitable for hunter-gatherers. Since the first systematic efforts of the Palaeolithic research in the Alborz Mountains by Carlton Coon in 1949 (1951, 1957), a few Palaeolithic sites have been discovered in the northern and southern slopes of the Alborz Mountains. Moving from the southern slopes of the Alborz Mountains towards the center of the Iranian Plateau, the number of Palaeolithic sites increases. Especially in recent years, many critical Palaeolithic localities have been identified on the interior plains of the Central Iranian Plateau (Biglari 2003, Masoumi et al. 2010, Eskandari et al. 2010, Vahdati Nasab and Feyz 2014, Vahdati Nasab et al. 2009, 2013, 2014, 2016, Heydari-Guran and Ghasidian 2011, Heydari-Guran et al. 2015, Kaboli 1999).
From the physio-geographical point of view, it seems that the sites located on the southern slopes of Alborz Mountain are related to the inner parts of the Central Iranian Plateau (Heydari-Guran et al., 2015). However, it has always been questioned whether the southern slopes of Alborz, like the northern slopes, were an area of human presence during the Palaeolithic. If so, was there a connection between the inhabitants of the southern and northern Alborz slopes? What about the connections to the inhabitants of the interior plains of the Iranian Plateau? Such questions led the authors to study the valleys located in the Southern Alborz Mountain foothills around 80 km crow flies to Tehran’s northwest. The survey in this region has led to the discovery of a complex of caves and rock shelters. The lithic artifacts from one site, Sorheh Rockshelter, presents new insights into the study of human settlement and behavior during the Late Pleistocene in the Iranian Plateau. 

Sorheh in the Palaeolithic Context of the Iranian Plateau
The Sorheh complex consists of 6 caves, and rock shelters were firstly identified in 2018 by one of the authors (H.H.). The complex is formed in a deep drainage system within tuff, shale, and sandstone lithology along the Senj River. It is located around 19 km north of the modern city of Karaj, at a longitude of 50,957,183 and latitude of 35,992,211, and approximately 1900 m above sea level. The first site of this complex on the west side of the valley, Sorheh Rockshelter, revealed rich Palaeolithic depositions. Preliminary examining the exposed strata and accumulated soil confirmed that the site is rich in archaeological remains.
Five other shelters of the Sorheh complex are located between 20 and 70 m east of Sorheh Rockshelter. They mostly consist of a rocky surface with poor deposition; some were destroyed by the looters’ pits. The bedrock dip in two rock-shelters is towards the front slope caused no preservation of archaeological deposits. The last shelter of this complex is attached to the Senj River and is endangered by periodically river flooding, thus empty of archaeological deposits. The newly-constructed road between the villages of Baraghan at the west to Vamkouh at the east destroyed partly two rock shelters; however, it provided easier access to Sorheh Rockshelter.
In general, the lithic techno-typological characteristics of Sorheh presents significant Middle Palaeolithic elements. These lithic artifacts bear little resemblance to their counterparts from Zagros, such as Warwasi, Bisetun, and Kunji (Dibble and Holdaway 1993, Dibble 1984, Baumler and Speth, 1993). However, a comparison with Zagros sites is not plausible because of the considerable distance between these sites and the Alborz. The sites located in the interior regions of the Iranian Plateau, perhaps, provide more relevant information. Most of the Central Plateau open-air sites, including Chah-e Jam, Mirak, Zaviyeh, and Holabad, are flake-oriented, and Levallois technology has widely been used (Heydari-Guran and Ghasidian 2011, Heydari-Guran et al. 2015, Vahdati Nasab et al. 2013, Vahdati Nasab and Hashemi 2016). Levallois technology was observed abundantly among Sorheh collection, though heavily retouched tools, reminiscent of the Zagros Mousterian, are nearly absent.  
Sorheh’s collection reveals more similarities to two open-air sites of Moghanak and Otchounak. The lithic artifacts from these sites are mostly based on the production of blades and elongated flakes (Berillon et al. 2007). The Levallois technology was broadly practiced in Moghanak and Otchounak. The points from Moghanak are plain and unretouched, reminiscent of the Sorheh points. Due to the lack of characteristic retouched tools in Moghanak and Otchounak, no typological comparisons were possible.

Conclusion
The evidence from Sorheh, Zagros Mountains, and the Iranian Central Plateau indicate various subsistence strategies in different geographical regions. This issue put forward the idea of cultural variability among the Middle Palaeolithic populations (Heydari-Guran et al., 2015) in contrast to the notion of cultural homogeneity (Mousterian) throughout the Iranian Plateau (Rosenberg 1988, Biglari et al. 2009, Piperno 1972). 
Considering the high elevation of 1900 m asl., Sorheh Rockshelter, after Ghaleh Kurd with 2100 m asl., is one of the highest-elevated Palaeolithic sites on the Iranian Plateau. Ghaleh Kurd has revealed Middle Palaeolithic artifacts assigned to the Mousterian techno-complex (Soleimani and Alibeigi 2012). The study of the deposits from Sorheh will provide valuable information on the climatic changes during MIS 5 to 3 up to Holocene. It seems that the area, despite high altitude, periodically provided ideal settlement conditions. Climatic amelioration intervals made the region suitable for settlement. Therefore, the detailed physiogeographic study of the Sorheh complex may provide a wealth of information on late Pleistocene climate changes.
Due to the techno-typological similarities of Sorheh lithics to the sites in the Central Iranian Plateau (Vahdati Nasab et al. 2013, Heydari-Guran et al., 2015), we hypothesize the cultural exchange between late Pleistocene hunter-gatherers of Alborz and the interior parts of the Central Plateau during climatic deterioration periods. 
The discovery of this complex with a particular geographical location in a valley with difficult access and, most importantly, the rich Palaeolithic depositions is an essential step towards answering questions related to the human dispersal at the edge of the Iranian Plateau during Marine Isotope Stages of 5 to 3 stages.
Systematic excavation and acquisition of more data in Sorheh will allow more accurate and detailed comparisons to other Middle Palaeolithic sites of the Iranian Plateau.