Fars Province has been the cradle of two great Persian empires—the Achaemenid and the Sasanian—throughout Iranian history. The presence of significant historical monuments from these two periods clearly demonstrates the importance of this province. One such region within Fars is Darab, which was home to the city of Darabgerd during the Sasanian period. Despite the historical and archaeological significance of this area within Iran, the amount of research conducted there remains limited. Given the importance of this city in the Sasanian era, this article seeks to clarify the position of the city and the khurrah (or kūra, “administrative district”) of Darabgerd and to reconstruct its defensive structure. Based on recent archaeological surveys in the Darab Plain, the study aims to determine the role Darabgerd played within the Sasanian administrative and political structure and to assess the duration of its importance. Furthermore, considering the fortresses and military fortifications surrounding the city of Darabgerd, the study examines how the defensive and monitoring system of the city and the Darab Plain functioned. At first glance, the ruins of Darabgerd—which testify to its former grandeur—along with the presence of a rock relief, a large and significant mint that remained active beyond the Sasanian period into the early Islamic centuries, and the discovery of seals and clay sealings, all attest to the importance of this geographical area during the Sasanian and early Islamic periods. For this reason, the existence of a coherent defensive structure for both the city of Darabgerd and the Darab Plain was essential. Based on the identification of fourteen fortresses during archaeological surveys of the Darab Plain, this research adopts a descriptive–analytical approach, integrating archaeological evidence with historical sources in order to provide a clearer understanding of the defensive structure of the Darab Plain during the Sasanian period. The results indicate that the geography of the Darab Plain played a decisive role in the formation of the city of Darabgerd and its defensive system.