Located in the easternmost part of Iran, Sista is the remains of an ancient state known throughout history under various titles such as Zaranka, Darangiana, Sakestan and Sistan. This region has evidence of settlements from the middle of the 4th millennium BC to the present, many of which are the remains of small and large ancient cities. Historical sources, from the Achaemenid Empire to the end of the Sassanid period, mention cities in the Sistan region that were the center of this eastern state during their own time, but the original location of many of them is now unknown. On the other hand, the lack of knowledge about these cities makes it difficult to study the urbanization process in this region. Therefore, in order to determine the original location of the main cities of Sistan in the historical period and to evaluate these cities structurally, the authors first intend to use historical approach to find the sites compatible with the mentioned cities in the historical sources; and then by specifying the architectural and urbanization features of each of these cities they investigate the urbanization process during the historical period of ancient Sistan. The results suggest that from the Achaemenid era to the end of the Sasanian period, five main and central cities were formed in Sistan, including Zarin , Prophthasia, Agriaspi, Ram Shahristan and Zarang, which correspond to the sites of Dahan-e Gholaman, Qala Farah, Qala Sam, Teppe Shahristan and Nadeali, respectively. The spatial structure and urbanization pattern have changed numerous times during this period, eventually leading to the emergence of large cities in the late Sassanid and the early Islamic period. The development of the urbananization process of Sistanand in the historical period can be regarded as the formation of the city of Zarang, which became one of the