The city of Susa, as one of the oldest urban centers in Iran, faced significant political, economic, and social ups and downs during the Sassanid period. Although written documents mark Shapur II's attack on Susa as the end of the city's life, archaeological data presents a more complex and dynamic picture of Susa's situation during this period. The present study aims to examine, based on the analysis of written sources and archaeological evidence, the factors that led to the rise and fall of the city of Susa during the Sassanid period. The main question of the study is what factors led to the Climax and decline of the status of Susa during the Sassanid period and how material evidence reflects these developments. The research hypothesis is based on the fact that Susa experienced relative prosperity in the early Sassanid centuries, especially during the reign of Shapur I, following the transfer of artisans from Antioch And the urban reconstructions that occurred and its ultimate decline were not the result of a sudden destruction, but rather the result of the centralization policy of the Sasanian state, the development of newly founded cities such as Gondishapur and Iran-Khore shapur, demographic changes, and political-religious restrictions. The research method is historical, descriptive-analytical, and comparative, and the data are analyzed based on written evidence from early Islam, such as travelogues and chronicles, Christian testimonies, and its combination with the findings of archaeological excavations in Susa, including architectural evidence, coins, seals, pottery, wall paintings, metal and glass works. The results of the research show that although Susa faced a serious crisis in the fourth century, archaeological evidence indicates that the city continued to be inhabited, active, and urban in nature until the late Sasanian period And decline is a gradual, structural process, not a sudden collapse.