Vaultings in Iranian Historical Architecture:A New Framework for Classification

Background and objectives: Vaulted coverings in historical Iranian architecture hold a central role in terms of form, spatial quality, and meaning, exhibiting a remarkable diversity compared to vaulted architecture in other architectural traditions. Throughout different periods of Iranian architecture, especially from the Islamic Middle Ages onwards, the shape and structural system of vaults continuously evolved, appearing in various forms and combinations across different buildings. Within this context, accurately identifying and categorising vaulting types is both essential and challenging. Accordingly, this study poses the question: ‘What is the appropriate framework for comprehensive and definitive identification and classification of vaults in historical Iranian architecture?’
Materials and Methods: To address this question, contemporary scholars’ viewpoints are examined through a descriptive-analytical method employing a twofold categorisation strategy. The first category encompasses studies in the field of Iranian historical architecture by scholars such as André Godard, Myron Bement Smith, Donald Wilber, Lisa Golombek, Mohammad Karim Pirnia, Gholam-Hossein Me’marian, and Hossein Zomorshidi. These studies introduce the theoretical geometry of vaults, their spatial relationships, construction methods, and applications, demonstrating the diversity of vault designs. Typically grounded in extensive fieldwork, these works align well with the characteristics of vaults in Iranian architecture; however, they generally do not propose a clear, comprehensive, and exclusive classification framework. The second category includes studies on structural systems by scholars like Robin Engels, Rowland J. Mainstone, and Bjørn N. Sandaker, who analyse and classify structural systems based on morphological features and structural behaviour. The thematic scope of these studies typically lies outside the realm of Iranian historical architecture. While this category offers a systematic and clear method for classifying vault structures by concurrently considering morphological and structural criteria, it lacks the necessary comprehensiveness, precision, and clarity to effectively address the diverse vaulting types in Iranian architecture.
Results  & Conclusion: This article proposes an integrated, novel framework for classifying vault types in Iranian architecture, synthesising findings from both categories through logical reasoning. This framework coheres with the remarkable variety of vault designs in historical Iranian architecture and, by simultaneously considering morphological and structural criteria, provides a clear methodology and rationale. Vaults are classified based on two concurrent criteria: the presence and configuration of structural elements and the form of these structural elements. According to the first criterion, vaults are divided into three groups: ‘without ribs,’‘with peripheral ribs,’ and ‘with peripheral and intersecting ribs. According to the second criterion, the vault is composed of brick shells (with an overall planar structural form) and ribs (with an overall linear structural form). Consequently, vaults consist of subcategories as follows: 1) Vaults without ribs featuring single-curved shells (barrel vault) or double-curved shells (squinch and domical vaults); 2. Vaults with peripheral ribs and single-curved shells (barrel), double-curved shells (squinch and domical, and Kajaveh), intersection of two single-curved shells (groin and crossed vault), or combinations of single- and double-curved shells (Khunecheh-poush); 3. Vaults with peripheral and intersecting ribs where shells are parts of single- or double-curved surfaces. These vaults are formed either through a sequential geometry of lines and planes (Karbandi vault), a sequential geometry of lines with non-sequential planes (ribbed vault), or a non-sequential geometry of lines and planes (Patkaneh or muqarnas vault).
Overlapping structural and morphological components forms the basis for dividing vaults into two categories: a) Planar vaults (including single-curved, double-curved, intersection of two single-curved shells, and combinations of single- and double-curved shells); b) Linear and planar vaults (which, depending on the sequential or non-sequential order of lines and planes, are subdivided into three groups). In planar vaults, the shell plays a central role as the main structural element responsible for stability and shape, whereas in linear and planar vaults, the shell’s role diminishes, and ribs primarily shape and stabilise the vault to the extent that this type of vault cannot be constructed without intersecting ribs. Accordingly, this article presents a systematic and integrated framework for identifying and introducing vaults in Iranian historical architecture by simultaneously considering morphological and structural components. Employing this framework not only offers a more comprehensive classification of vaults but also reveals challenges faced by designers and builders of vaulted structures, thereby opening a new window for designing innovative vaults in the contemporary architecture.