The Tehran-Semnan (Khorasan) route, as one of the principal ancient communication corridors in eastern Tehran Province, played a significant role in Iran’s economic, cultural, religious, and military networks throughout the Late Islamic centuries and constituted an integral segment of the Greater Silk Road. Until recent decades, scholarly knowledge of this route relied primarily on brief references preserved in historical texts dating from the 3rd to the 7th centuries AH; however, the arrival of European travelers and the subsequent publication of travel accounts considerably expanded available information. This study employs a combined analysis of historical sources and systematic archaeological field surveys to reassess the spatial configuration of the route, as well as the formation processes and functional characteristics of its associated roadside architectural and infrastructural remains as material archaeological evidence. The research addresses two principal questions: first, which factors contributed to the establishment and development of the Tehran-Semnan (Khorasan) route during the Late Islamic period? Second, how did this route interact with other ancient routes within Tehran Province in shaping the pilgrimage networks known as the Atabat-e Aliyat routes? Adopting a descriptive–analytical methodology, the study integrates archival research with archaeological investigations. The results demonstrate that geographical setting, commercial activity, and, in particular, political and religious considerations played decisive roles in the formation, continuity, and long-term significance of this major ancient communication corridor, leading to the construction of extensive roadside infrastructures along its course.