The Evolution of Semi-Open Spaces in the Architecture of Historical Mosques in Khorasan

Semi-open spaces, which act as transitional elements between open and enclosed spaces, play a central role in the spatial organization of many Iranian mosques. These spaces are not only important in terms of climate responsiveness and functional use, but also have a significant impact on the architectural identity and formal expression of mosques. Previous studies have shown that semi-open spaces in mosque architecture help to modulate climatic conditions and increase the flexibility and multifunctionality of the building by creating spatial hierarchy. However, the historical evolution of these spaces has received limited comprehensive attention. This study aims to investigate the semi-open spaces used in the architecture of historical mosques throughout the Khorasan region, within the contemporary borders of Iran, and based on a chronological sequence. This research uses a descriptive-analytical method based on field and library studies. To ensure the reliability of the findings, all historical mosques of Khorasan registered in the National Heritage List of Iran have been analyzed. The samples include 151 historical mosques from the early Islamic centuries to the Pahlavi era. These mosques are scattered across the three provinces of North Khorasan, Razavi Khorasan, and South Khorasan. The findings indicate that the transformation of these spaces occurred either through gradual modification of previous forms or through the emergence of new types of semi-open spaces in mosque architecture. From the early Islamic centuries to the Seljuk era, these spaces were mainly manifested as surrounding porches. A major turning point occurred in the Khwarezmian period with the replacement of porches with deep, high iwans, a development that continued in the Timurid and Safavid periods. Notably, the emergence of columned halls (satavand) during the Timurid period, which continued until the Pahlavi period, marks another evolutionary stage. However, from the Safavid period onwards, a significant decrease in semi-open spaces is observed, culminating in the Qajar period, where courtyard-style mosques became the dominant design.