evidence newfound of the Sassanid presence in the Central Plateau (evaluation of archaeological evidence and written texts) Case Study Shirkooh area Nain

1.Introduction
The location of Isfahan province in a highway which connects the north to the south and the east to the west has created a suitable situation for transformation and innovation of art and architecture. Naein in Isfahan province is a town located in the desert margin. Pakooh region is one of the villages of Naein located in the northwest. The ancient site of Shirkooh is in the vicinity of Separo Village located 6 kilometers away from the west of it. Due to its strategic location, this region has always been suitable for human settlements. Among the evidence which represents a Sassanian settlement in Shirkooh, one can mention a fortress, a Čahārṭāq (four arches), and Soffeh (Terrace platform).It is likely that in the past this region was located near a major communication highway. Hence, the Sassanid constructed a fortress on top of Shirkooh (Zardkooh).
 
2. Methodology
The method of research in this paper is descriptive-analytical and data collection has been established by conducting a field survey and studying written documents. Using the second method, all information and data related to this paper, including historical texts and particularly geographical accounts, have been collected. By archaeological survey, architectural structures and cultural materials such as wares completely studied and documented. Then both data evaluated which made Comparative studies and relative chronology possible.
 
3. Discussion
By studying the historical texts, we recognize that the state of Fars was not only a religious and political center but also officially important for the Sassanid dynasty. During the reformation of Khosrow I, Iran was divided into four sections. 1. Kust-e-xwarasan, northeast part؛2. Kust-e- xwarwaran, Southwest part؛ 3.Kust-e- Nimruz, Southeast part; 4. Kust-e- Adurbadgan, northwest part (Daryaee, 2009: 21-24).
 According to some credible historical texts like Šahrestānīhā ī Ērānšahr Fars state was located in one of these sections called Kust-e- Nimruz. Based on some geographers of the early Islamic Centuries like Ibn Hawqel, Abu Abdallah Jayhani, and Istakhri, Fars was one of the most extensive states which was divided into five Kura and Naein is considered to be a town in Kura of Istakhr. (See also Istakhri, 1970: 15; Ibn Hawql, 1966: 34; Jayhani, 1989: 111).
One of the most important evidence to complete the knowledge of existing historical sources about the presence of the Sassanid in the Central plateau of Iran can be obtained through archaeological studies. Although systematic studies haven’t been carried out in this region yet, some sporadic archaeological surveys indicate the existence of different historical periods, most notably in Shirkooh, a village located in the northeastern part of Nain. During this survey, archaeologists found a site consisting of a Čahārṭāq, a fortress, and a Soffeh which date back to the Sassanid and early Islamic era. The aim of this paper is to discuss these three important architectural structures.
 
Čahārṭāq (Four arches)
Čahārṭāq and fire-temples are among the most important archaeological and yet controversial structures of the Sassanian architecture. The Čahārṭāq of Shirkooh, located in the central part of Naein, can also be placed in this category. In 2002 the building was listed as a national property of Iran with the registration no. 7222 and after that, it was restored by Shah-Hosseini (Shah-Hosseini, 2002: 327). The Čahārṭāq of Shirkooh is a square-shaped structure with approximate dimensions of 10 meters. Its current height is 12/40 meters, dome height is 6/10, and the internal height is 6/59 (Namjoo, 2013: 172). The architectural elements of Čahārṭāq consist of piers, arch, squinch, and dome. The interior has no special decoration, but remains of plasterwork could be seen in some parts of the squinches. Studying wares and plan of the building, we could say that this Čahārṭāq dates back to the Sassanid era. The well-known types of wares are bowls with smoothed or inverted rims (samples 2 and 3) comparable to wares of Chal-e-Tarkhan, Tel Abu-Sharifeh; and jars with quartet rounded rims (sample 4) can be compared with wares of Farsan (Khosrozadeh, 2014: figs. 83-5).
 
Shirkooh fortress
The position of this fortress is in such a way that on top of it the Čahārṭāq is visible and on the other hand, the fortress is pretty obvious from the center of Čahārṭāq. Thus, these two structures are not far from each other. The fortress is constructed in the mountainous north of Shirkooh village. The plan of the fortress is almost irregular and a steep slope makes it hard to reach. The materials used in the construction of the fortress are cobblestones for the walls, mud-brick in towers and plaster as the main mortar of the entire building. At the interior of the fortress there is a rectangular structure which its directions are north-east south-west and somehow overlooking the low level of the plain and the village. The dimensions of this rectangular structure are 8 × 2 meters (Alian, 2007: 17). Due to unauthorized excavations inside the fortress, a piece of plasterwork was found; this piece is 16 cm long and 9.5 cm wide and its surface is engraved.
The type of design, which is likely to be two-dimensional, could have been used as part of a plaster pillar or Qarniz (baseboard). It should be noted that due to a lot of damages it is not easy to discuss this piece. The side section has two vertical lines with two rows of pearls in the shape of laced circles. The main part of the design has also two waves motifs One up and the other down.
Terrace platform of Shirkooh (Soffeh)
Terrace platform is located at 38 7.33 N, 52 59 24 E (Aliyan, 2007: 21). It is constructed at the farthest end of the site which connects it to the mountain. The main construction material of this Soffeh consists of cobblestones of the river. Since this terrace platform is flat and elevated, from the top of it the fortress and Čahārṭāq are remarkably visible.
Unfortunately, many unauthorized excavations have been carried out the site that can be considered as the most important factor in the destruction of the surface of the terrace platform. It should be noted that during the survey of Soffeh we haven’t found any cultural materials like wares. Overall it can be said that the most significant materials used in these structures (Čahārṭāq, fortress and terrace platform) are cobblestones and plaster mortar. Mud-brick was only used constructing fortification towers, while the plaster widely used for decorating and coating the walls of the fortress.
 
3. Conclusion
Based on the information obtained from the Muslim geographers and historians, Shirkooh region was under the cultural-political supervision of Istakhr, known as the northernmost Kura of Fars. The mountains of the Shirkooh region are naturally considered as an enclosure to cover the site from the world outside. Shirkooh fortress was built on top of a relatively steep and impassable mountain placed at the northernmost part of the site.
The plan of the fortress is approximately irregular because of the natural shape of the mountain. It is pretty obvious that the most important cultural material that exists in most of the sites and plays a crucial role in chronology is ware. The comparison of potsherds of Shirkooh fortress with samples of Chal-e Tarkhan at the central plateau of Iran, Qal'eh Yazdgerd at the west (Kermanshah province), Oltan Qalasi at Mugan plain, Hajiabad at Fars, Tureng Tepe at Gorgan , Tel Abu-Sharifeh at Iraq, indicates that the cultural materials of this site belongs to the Sassanid era. We believe because of the existence of a military fortress and a religious complex (Chartaghi) both close to a communication highway which connects south to the north and west to the east, Shirkooh must have been a principal site of the Sassanid era. Considering that the interior of the fortress is not so large, it might have been used as a military or road controlling fortress. We hope more archaeological research helps us expand our knowledge of the site, especially obtaining an absolute dating through interdisciplinary studies.