Archaeological studies of ancient cities have a significant role in understanding their formation, their development, the fall and destruction in different historical periods. According to the historical sources (the 10th to 14th century A.D) there has been an ancient city named Shapurkhast on the western of Iran, which its history dates back to Sasanian era. In these sources, the city has constructed by Shapur I (240-272 A.D). Life in the city had continued during the Islamic period until the 14th A.D. The city reached its peak in the 11th century AD. The remnants of the old city have been founded at south-eastern parts of the modern city of Khorram Abad especially from the excavations in 2007. The present research analyses the data derived from the historical resources and archaeological evidences in order to study and investigate the factors in settling in the area. This study deals with the formation, development and prosperity and then the fall of Shapurkhast city. The results of this study imply that the main period of occupation of Shapurkhast was Islamic era that its foundation has been made at pre-Islamic periods, and probably even Parthian era. Having appropriate environmental conditions and also lying at the middle of west to east and north to south communication routes, the south plain of Khorram Abad has potentially provided suitable living conditions for forming the city. It seems that Shapurkhast has been abandoned at the 13th or 14th A.D and modern Khorram Abad began to function as the central town of the region. Environmental and ecological conditions are the most important factors for the collapse of the city.
The present study is based on a "holistic" approach and based on two categories of historical and archaeological information which has provided new information about one of the early Islamic cities in Iran. The data is based on historic sources from the 10th to 14th AD, and archaeological evidences from the excavation at southeastern Khorram Abad in 2007 and then archaeological surveys at Khorram Abad gorge in 2000 and 2016.
The most important questions in this research are the following:
1. When did the settlement in the city of Shapur Khasta begin and what were the reasons for the formation of the city?
2. In what period and based on which components are the peak of prosperity and urban development introduced?
3. What were the factors that cause the collapse and fall of the city in the Middle of Islamic period and the transfer of its population to the northwest of the town?
The research hypothesis is that Shapurkhast city was an important early Islamic city, which its foundation was made before of Islamic period. There has not been much research about the city of Shapurkhast from the formation to the fall. Additionally, available researches are relatively old and no new comprehensive research has been done on the city with archaeological viewpoint, and some of the reports have not been published. Therefore, we will try to use archaeological evidences, written sources and the historical maps aiming to provide suitable information about one of the unknown cities in Iran.
Urban development and urbanization was formed as a manifestation of the power of the Sassanid Empire in Iran and in competition with the Roman Empire (Moqimizade, 2017). the development of urban settlements has been subject to environmental, economic and social conditions; That is, urban settlements were centers of communication, recreation, and redistribution of commercial goods to subordinate cities and states. Around the city of Shapurkhast; Suitable ecological substrates including important Zagros highlands around, rich water resources especially KhorramAbad and Karganeh rivers, flat and fertile plain south of the valley, and most importantly being located in the east-west and north-south communication routes from The main factors in the formation of settlements in the south of Khorramabad valley, followed by the formation of urban settlements. We know very little about the formation of the city. Due to the development of the Silk Road in the Parthian period and the location of the city in the communication routes east and west of the region and south to north, the urban life of Shapurkhast city probably took place in the Parthian period. Due to the existence use of the name "Shapur" in archaeological evidence, this city was developed during the Sassanid period. The existence and permanence of the king's name on the coins (Figure 14) left over from the Sassanid period certainly indicates the double and strategic importance of the city in the Sassanid period, which proves the Sassanid rule in these areas. The distribution of Sassanid sites in the Khorramabad valley is another proof of this claim (Figure 4). Our knowledge indicates that the first time, Sassanid Shapur in order to develop individual power to urban development for change the social structure of Iran, cities has undergone changes and developed and in this process the name "Shapur" on most cities as Shapurkhast "was established. Archaeological evidence from the excavation does not prove that urban development is a process, meaning that urban development has been accompanied by ups and downs. Among the reasons could be the decline of the Sassanid rule and repeated invasions of Iran. In the Islamic period from the fourth and fifth centuries onwards, when the Seljuks ruled in the Middle East in Iran, Iraq, and Asia Minor; the golden age of prosperity and development of the city began and the Seljuk’s (10th to 12th AD) of Iraq made Khorramabad one of the most important strategic points and connections with the Seljuks of Iran. The granting of coins to Al-Hasnawiyah and the existence of local coins were minted in the name of local governors clearly and significantly increase the importance of the city. In the Islamic period, this city has completely passed the urban life and has had a mosque, a mint and a government fortress. Due to its importance, the city has been repeated many times in geographical and historical books.
Based on the holistic mentality in this study, important information is provided; from written historical resources including geographical and historical books and data from archaeological excavation find such as coins, pottery and the distribution of sites regarding the formation, development and fall of the city of Shapurkhast (Figure 10 and 12). The foundation of the mentioned city was laid in the Parthian period. The city was developed during the Sassanid period due to the importance of the Sassanid kings in the development of cities and their location on trade routes, and was named after Shapur, the second and most powerful Sassanid king. In the Islamic period, after a short break, we see the comprehensive development of the city and the benefit of all urban structures, especially in the Seljuk period. The city was still prosperous until the end of the 14th century AD, when due to the growth of the town of KhorramAbad, its inhabitants merged with the current KhorramAbad and continued urban life. This city has been developed with suitable environmental conditions and being located on ancient roads and has been one of the important cities of the region in the Islamic era. During the patriarchal period, ecological and environmental conditions were among the most important factors in the abandonment of the city.