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.

1. Introduction
The Tehran-Semnan (Khorasan) highway represents one of the most significant ancient communication corridors in the eastern part of Tehran Province, forming an integral segment of the greater Silk Road network. Throughout the late Islamic centuries, this route played a pivotal role in Iran's economic, cultural, religious, and military spheres, facilitating the movement of goods, pilgrims, armies, and ideas between the central plateau and the eastern provinces of the country. Until recent decades, scholarly knowledge of this highway was primarily derived from brief references preserved in historical and geographical texts dating from the 3rd to the 7th centuries AH. These sources, including works by authors such as Istakhri, Ibn Hawqal, and Yaqut al-Hamawi, provided only limited information regarding the number of waystations and the distances between them. However, from the beginning of the late Islamic period, the arrival of European travelers and the subsequent publication of their detailed travel accounts significantly expanded available information, offering richer descriptions of the route's infrastructure, waystations, and surrounding landscapes. The city of Rayy, as a major urban and commercial center, served as the starting point of this highway, with its eastern gates, particularly the Khorasan Gate and Dulab Gate, providing access to the route. Over time, particularly during the Safavid and Qajar periods, the expansion of Tehran led to the establishment of new gates, such as Dushan Tappeh, which also facilitated access to this important road. The highway's significance was not merely commercial; it also served as a vital link for pilgrimage networks, including the routes to the holy city of Mashhad and the Atabat-e Aliyat (the shrine cities of Iraq). This study aims to reassess the spatial configuration of the Tehran-Semnan (Khorasan) highway, as well as the formation processes and functional characteristics of its associated roadside architectural and infrastructural remains, by integrating historical textual analysis with systematic archaeological field surveys. The research addresses two principal questions: first, which factors contributed to the establishment and development of this highway 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?

2. Research Methodology
This study adopts a descriptive-analytical methodology, integrating archival research with archaeological investigations. The research process began with a comprehensive review and analysis of historical texts, travelogues, and historical maps. These sources included medieval geographical works, European travel accounts from the 19th century, and later Persian-language travel narratives. Subsequently, systematic archaeological field surveys were conducted along the identified route to locate, document, and analyze the physical remains of roadside structures, including caravanserais, water reservoirs, watchtowers, bridges, and other infrastructural installations. The archaeological data were then compared and correlated with the historical textual evidence to accurately determine the route's alignment, identify the locations of waystations, and assess the functions and construction periods of the associated structures. This combined approach allowed for a more reliable and comprehensive understanding of the highway's spatial configuration, its developmental trajectory, and its multifunctional role within the broader communication network of the region. The use of GIS tools facilitated the spatial mapping and analysis of the route and its associated features, enabling a clear visualization of the highway's connection to other major routes in Tehran Province.

3. Discussion
3.1. Factors Contributing to the Formation and Development of the Highway
The analysis of historical and archaeological data reveals that the formation and development of the Tehran-Semnan (Khorasan) highway during the late Islamic centuries were influenced by a combination of interrelated factors. Foremost among these was its strategic geographical setting. The city of Rayy, located at the junction of major routes, served as a central hub, and the highway's path across the southern foothills of the Alborz Mountains provided a relatively accessible corridor to the east. Secondly, the highway's commercial significance as a vital section of the Silk Road was paramount. It facilitated the transit of a wide range of goods, including silk, textiles, carpets, spices, and precious stones, between East and West, thereby contributing to the economic prosperity of the regions it traversed. Thirdly, political and religious considerations played a decisive role. The Safavid and Qajar governments, in particular, invested heavily in the construction and maintenance of roadside infrastructure to support their political ambitions, facilitate the movement of armies, and, importantly, promote religious pilgrimage. The Safavid state, in its rivalry with the Ottoman Empire, actively encouraged pilgrimage to the shrine of Imam Reza in Mashhad as an alternative to the Hajj, leading to substantial investment in the Tehran-Khorasan route to enhance the safety and comfort of pilgrims. These combined factors led to the construction of extensive roadside infrastructures along the course of the highway.
3.2. The Highway within the Road Landscape (Manzar-e Rah) Framework
The study applies the concept of "road landscape" (manzar-e rah), which encompasses three interrelated dimensions, to analyze the highway's infrastructural and functional organization. The first dimension is the residential-welfare landscape (manzar-e eghamati-refahi), which comprises essential structures such as caravanserais, water reservoirs (ab anbars), and other facilities designed to provide shelter, rest, food, and water for travelers, pilgrims, and merchants. These installations were strategically placed at intervals of approximately one farsakh (roughly 6 kilometers) or one stage, reflecting a systematic planning approach to meet the needs of caravans. The second dimension is the directional landscape (manzar-e hedayati), consisting of wayfinding elements such as towers or minarets (mil) built between waystations to guide travelers and help them navigate the often featureless terrain. These structures served as landmarks, indicating the correct path and preventing caravans from losing their way. The third dimension is the mobility-security landscape (manzar-e harekat-amniati), which encompasses the physical infrastructure for movement, including the road surface itself, bridges, mountain passes, and also security-related installations such as watchtowers and post houses (chaparkhaneh). These elements were crucial for ensuring the safe and efficient transit of people, goods, and information. The Tehran-Semnan highway, with its comprehensive array of these features, exemplifies a fully developed historical road landscape.
3.3. Historical Texts and Travel Accounts
References to the Tehran-Semnan (Khorasan) highway in medieval Islamic geographical texts, such as those by Jayhani, Istakhri, and Ibn Hawqal, are brief, primarily listing waystations and distances between them. These sources typically mention stations such as Afrandin, Kahandeh, Deh Namak, and Semnan, indicating a well-established route. However, the most detailed descriptions come from European travelers of the 19th century. For example, Edward Backhouse Eastwick, who traveled the route in 1864, provided vivid accounts of the waystations, including Khatunabad, Kabud Gonbad, and Eyvanaki, describing their infrastructure, such as caravanserais and watchtowers, and offering critical observations on their often-poor condition. Similarly, George Nathaniel Curzon and the Japanese monk Suzuki Shinju provided detailed statistics on the number of waystations and total distance, which allowed for the reconstruction of the route's precise alignment and a comparison with archaeological evidence. These accounts not only confirm the route's importance but also offer valuable insights into its functional state during the late Islamic period.
3.4. Archaeological Evidence and Waystation Analysis
Systematic archaeological surveys conducted by the authors, combined with previous research, have identified and documented numerous roadside structures along the Tehran-Semnan highway. The first major waystation in the vicinity of Tehran is the Qajar-era Khatunabad caravanserai, built in 1238 AH (1822 CE) by Molla Ali Kani to provide refuge for pilgrims traveling to Mashhad. Further east, at Kabud Gonbad, the remains of a Safavid four-iwan caravanserai and a guide tower were documented. The Safavid Shah Abbasi caravanserai at Eyvanaki is a particularly notable structure, characterized by its robust four-iwan plan, with architectural features designed for both security and comfort. The site of Deh Namak stands out for its concentration of infrastructure, including two caravanserais, three water reservoirs, a watchtower, and a historical fortress, all dating primarily to the Safavid and Qajar periods. This concentration underscores the site's strategic importance at the junction of the Tehran-Khorasan highway and the road from Isfahan to Firuzkuh. Finally, the Lasjerd and Dehaqin caravanserais, located near the boundary with Semnan Province, complete the chain of major waystations within Tehran Province. The architectural analysis reveals a consistent use of materials such as brick, stone, gypsum, and lime mortar, adapted to the local climate. Features such as corner watchtowers, central courtyards, and separate quarters for servants and animals reflect a clear understanding of the diverse needs of travelers, ensuring both safety and a degree of comfort despite the harsh desert environment.
3.5. Connection to the Atabat-e Aliyat Routes
The research confirms that the Tehran-Semnan (Khorasan) highway, together with the Tehran-Qom and Tehran-Saveh highways, constituted the primary pilgrimage routes of the Atabat-e Aliyat network in the Tehran Province region. While the Tehran-Qom and Tehran-Saveh routes led southwest to the holy shrines in Iraq, the Tehran-Khorasan highway facilitated pilgrimage to the holy city of Mashhad. This network of routes was deliberately developed and promoted by the Safavid state as a means of consolidating Shi'a identity and providing an alternative for pilgrims who could not undertake the difficult and often dangerous journey to the Hejaz. The interconnectedness of these routes meant that a pilgrim or traveler could journey from Isfahan or other southern cities via Qom or Saveh and then, from Rayy or Tehran, join the Khorasan highway to travel east. This integrated network highlights the region's role not just as a commercial thoroughfare but as a crucial artery for the religious life and political integration of the Safavid and Qajar empires.

4. Conclusion
The Tehran-Semnan (Khorasan) highway was far more than a simple thoroughfare; it was a complex, multifunctional corridor that played a vital role in the economic, cultural, religious, and political life of Iran during the late Islamic centuries. The integration of historical texts, European travelogues, and systematic archaeological surveys has allowed for a detailed reconstruction of its route and a comprehensive understanding of its significance. The highway's formation and development were driven by a combination of geographical, commercial, political, and religious factors. Its infrastructure, as evidenced by the extensive network of caravanserais, water reservoirs, watchtowers, and post houses, was designed according to a systematic "road landscape" model to address the needs of travelers, merchants, pilgrims, and soldiers. The findings confirm that the highway was a key segment of the Silk Road, a principal route for pilgrimage to Mashhad, and an integral part of the Atabat-e Aliyat network, connecting Tehran to other major routes. The majority of the identified structures date to the Safavid and Qajar periods, reflecting the strategic investments made by these dynasties to control, secure, and economically and religiously benefit from this vital communication artery. Ultimately, this study demonstrates that the Tehran-Semnan highway is a prime example of a major historical route whose significance was rooted in the convergence of diverse commercial, religious, and political functions, making it a cornerstone of the region's historical landscape.