Dome on Squinches: an Innovation in Construction Technology of Ancient Iran

Online Journal of Engineering Sciences and Technologies (OJEST) ISSN: 2588-6770; www.ojest.ir

Vol. 2, No. 1; Winter 2019; Pages 1-4; DOI: 10.21859/ojest-02011

Dome on Squinches: An Innovation in Construction Technology of Ancient Iran

Elham Saligheh Department of Architecture, University of Tabriz, Tabriz, Iran. Nasibeh Badri Benam Department of Architecture, Tabriz Branch, Islamic Azad University, Tabriz, Iran.

Received 1 February 2019 Accepted 15 March 2019 Available Online 30 March 2019

ABSTRACT Innovation in structure and construction technology was one of the valuable achievements of ancient architects all over the world. There was no structural separation of architectural elements in the ancient buildings of Iran. Domes are of among the important innovations in ancient architecture that were usually built over important spaces or in special buildings. The three dimensional form of dome was a tool to distinguish the significant building from other routine buildings in a city and turn it into a landmark in the urban silhouette. Iranian master builders had introduced an architectural innovation which had an imperishable effect on dome technology in the Middle East and Central Asia; surmounting a dome on squinches. The present study is an overview on the nature and function of squinche and the construction process of vaults and domes built on squinches. Several significant buildings constructed by the mentioned technology are also introduced in this article.

Keywords: construction; dome; squinch; vault.

Introduction Domes differ considerably in type and shape. Persian Innovation has always been the most important driving domes and vaults are commonly well-known due to their force in design and construction of built environment, various typologies, proportion of components, specific especially dominant buildings in ancient civilizations all forms, and graceful designs. In this article, a particular across the world. Therefore, the innovative combination type of dome built on squinches, its root and technical of structure and form has brought about a composition characteristics, was introduced and analyzed. of technology, art and aesthetic in all ancient buildings. This achievement was possible by a smart combination Squinch Vaults of structural knowledge, construction techniques and The squinch vault represents the structural and acquaintance with materials and their behavior. The fact technical concepts of the Sassanian vaults. This that architecture comes into being only in combination sort of vault is also known as ‘khorassani’ due to the with structure made the consideration of foundation, geographical area where it is more commonly found columns, and ceiling inevitable in all ancient buildings. (north eastern Iran), or even “balkhi” in reference to the In different eras, architects paid a significant attention to city of Balkh (now called Mazar-i Sharif, Afghanistan). the rules of loading, position and function of supports, The construction process of this vault started with a and their connection with other structural elements, small arched course laid in each corner of a square room, diminishing the forces in the walls leading to elimination advancing with new and increasingly larger arches of unnecessary mass, physical elements and reduction of leaning on the previous ones, defining thus four corner weight. half-cones that met in the center of each side of the room Vaults and domes were the among the most important as illustrated in Fig. 1 (Herrmann, 1999). The remaining elements in Iranian buildings until the beginning of the square opening could be covered by continuing in the 20th century. The fundamental contribution of Persian same way, as it is done still now in Khorassan area, or by architecture in dome development in the Middle East re-starting the process from the newly created corners. and Central Asia was first due to establishments of Squinch vaults were apparently hardly ever used in the foundation for using masonry domes to cover the early Islamic monumental structures, as no examples chamber halls, and second, the unique innovation of from this period has survived. The only surviving vaults an approach for transferring from the square geometry are later. In the eastern part of Iran, there exists some to the circular one, namely, squinches which mainly examples in Khorassan (and neighboring countries appeared in the Sassanid period. Dome was the certain like Turkmenistan & Afghanistan) houses and in element of Persian architecture which was widely used, the congregational mosques at Isfahan (Copani & elaborated and developed after the advent of Islam. Buonanno, 2003). 1 Correspondig Author: [email protected] Online Journal of Engineering Sciences and Technologies (OJEST) ISSN: 2588-6770; www.ojest.ir Saligheh & Badri Benam, 2019

Fig. 1: Construction process of squinch vault (Herrmann, 1999).

Squinches with Step Form Fig. 3: Dome on squinches (Reuther, 1939). These types of squinch domes are related to concept of squinch-vault. In these cases, the squinch does not In the dome over squinches in the “Sassanian palace” need anymore to span the corner of a square room but at Sarvistan, Iran (Bier, 1986), the transition section, small sections of an already circular plan, becoming thus formed by the drum with the squinches, was made of almost a true spherical surface. The decorative effect of cobbles and roughly cut stones embedded in gypsum this solution, similar to a scale-pattern, would gain a mortar (as are most of the building’s walls), but the decorative value by itself (Fig. 2). dome itself was built with bricks (Fig. 4). Meanwhile, in the dome over squinches at the Ardashir’s Palace in Firuzabad, the squinches and the dome were both built with cobbles embedded in gypsum mortar (Fig. 5).

Fig. 2: Stepped squinch dome and ‘scales’ pattern and springers of spherical vaults (Reuther, 1939).

Domes on Squinches In many ways, the Sasanian period of ancient Iran, witnessed the peak of construction innovations and achievements. The Sasanians' cultural influence as well as construction technology innovations extended far beyond the empire's territorial borders. In fact, much of Fig. 4: Dome of Sarvistan palace (www.panoramio.com). what later became known as Islamic civilization in Iran, were taken from the innovations and achievements of Persians into the wider Muslim world (Taghizade, 2012). The Sassanian-originated dome on squinches can be seen as a particular case of the squinch vault described above. In this case the four corner half-cones (or half- conoids, if its profile is a parabolic one) are not carried to the middle of the room, leaving some space between them that is filled with horizontal courses, until a horizontal circle is made at the crown of the squinch arches, on which the dome will rest. The dome has a half-elliptical section and is built with horizontal circular courses, without using centering, by means of gypsum Fig. 5: Dome of Ardashir’s palace in Firuzabad (www.flickr.com). mortar (Fig. 3). 2 Online Journal of Engineering Sciences and Technologies (OJEST) ISSN: 2588-6770; www.ojest.ir Saligheh & Badri Benam, 2019

Domes Supported by Lintelled Squinches constructed on the ground (Pasic & Siravo, 2004; Unsal, A singular case of lintelled squinches was recently 1973). Pendentive is a triangular section of vaulting discovered, at the Amman citadel palace, supporting the between the rim of a dome and each adjacent pair of the dome over the throne hall (Arce, 2000). arches that support it. Any of these triangular sections of This element was composed of several stone-cut vaulting, positioned at a corner of a rectangular space to elements (Fig. 6). First, the ones forming the “beam” support a circular or polygonal dome. From construction or squinch lintel itself, originally a timber beam, that point of view, the difference between squinch and translated into stone by stonecutters, becomes a three- pendentive is shown in Figs. 7 and 8. piece flat arch. It was composed of two lateral corbelled pieces embedded diagonally into the wall corners, and a key stone that fits between the two corbels with a joggled joint (Arce, 2006).

Fig. 7: Dome construction process on squinches (Pendentives and Squinches, 2020).

Fig. 8: Dome construction process on pendentives (Pendentives and Squinches, 2020). Fig. 6: Domes on lintelled squinches. Amman Citadel Throne hall (Arce, 2000). Discussion and Conclusion Iranian architecture has a long continuous history that These elements, due to their wooden origin, were dates back to more than 6,000 years ago. Still, it doesn’t decorated with a semicircular molding in their lower fail to fascinate designers and engineers with both its section and with a couple of rolling corbels in the areas aesthetic and technological value which was considered close to the wall. In their back face, they present a recess to be magical. Each one of the historic periods of ancient to support the coffered triangular slab that serves as a Iran including Elamites, Achaemenids, Parthians, and ceiling for the space spanned by this composite lintel. Sassanids were creators of influential innovations in Traces of the stone carved cornice, recalling also a construction technology that over the ages has spread Sassanian pattern of teardrops, that was placed at the wide all over other civilizations and far to other cultures base of the dome was retrieved from the site as well. being adopted. The dominant buildings of ancient Iran Most probably, the dome on top of these squinches display a great variety, both in structural innovations was built with a Sassanian technique using cobbles and aesthetic ideas, developing gradually and coherently embedded in gypsum-based mortar, and with a slightly out of prior traditions and experiences. Without sudden parabolic section. Antecedents of this element are still innovations, and despite the repeated trauma of invasions nowadays a standard roofing system in the Northern part and cultural shocks, it has achieved individuality of Iran and the neighboring regions such as Azerbaijan, distinct from that of other neighboring civilizations. Its Georgia, Armenia and Tajikistan (Arce, 2000). paramount virtues created a marked feeling for form, harmony, scale and structural innovation, especially in Pendentive vs Squinch vault and dome construction. Even though the term dome has been used similarly Sassanid architecture refers to the Persian in different literatures both in the Eastern and Western architectural style that reached a peak in its development architecture, there has been a major architectural contrast during the Sassanid era. In many ways, the Sassanid between the compositions of its spatial elements. While dynastic period (224-651 CE) witnessed the highest eastern domes were supported on squinch, western achievement of Persian civilization, and constituted the domes were systematically erected on pendentives. last great Persian Empire before the Muslim conquest. The main attribute of pendentive dome’s construction In fact much of what later became known as Islamic is that it does not require column and beam construction. architecture were taken from the Persians into the wider The upper dome is supported in either ways, by round Muslim world. During this period, the most essential arches or a dome-base structure. The upper dome can innovation was the concept of dome and its technical be constructed on the arches instead of being directly 3 Online Journal of Engineering Sciences and Technologies (OJEST) ISSN: 2588-6770; www.ojest.ir Saligheh & Badri Benam, 2019 nature with the construction of semi-elliptical domes which were often erected on reception or ceremonial halls of palaces. The Persians solved the problem of constructing a circular dome on a square building by the utilization of squinch. After this era, and even nowadays architects can use this historic innovation to construct the buildings with wide spans.

References • Arce, I. (2000). The Umayyad Congregational Mosque and the Souq Square complex at Amman Citadel. Architectural features and urban significance. Proceedings of the 2nd, International Conference on the Archaeology of the Ancient Near East- 2 ICAANE, Copenhagen. • Arce, I. (2006). Qasr Hallabat (Jordan) revisited: Reassessment of the material evidence. In H. Kennedy (Ed.), Muslim Military architecture in Greater Syria. Leiden: Brill. • Bier, L. (1986). Sarvistan: A study in early Iranian architecture. University Park, Pennsylvania, United States: Penn State University Press. • Copani, P., & Buonanno, L. (2003). The «Cuba» near Castiglione in Sicily, a self supporting vault made of volcanic stone. First International Congress on Construction History, Madrid. • Herrmann, G. (1999). Monuments of Merv: Traditional buildings of the Karakum. London, United Kingdom: Society of Antiquaries of London. • Pasic, A., & Siravo, F. (2004). Reclaiming Mostar’s monuments and buildings. In Conservation and revitalisation of historic Mostar. Geneva: The Aga Khan Trust for Culture, 47-56. • Pendentives and Squinches. (2020). Essential humanities. Retrieved from http://www.essential-humanities.net/art- supplementary/pendentives-squinches/ • Reuther, O. (1939). Sassanian architecture. In A. U. Pope, & P. Ackerman (Eds.), A survey of Persian art from prehistoric times to the present (pp. 493-578). London, New York, NY: Oxford University Press. • Taghizade, K. (2012). An investigation of historical structures in Iranian ancient architecture. Architecture Research, 1(1), 1-7. doi: 10.5923/j.arch.20110101.01 • Unsal, B. (1973). Turkish Islamic architecture in Seljuk and Ottoman times 1071-1923. London: Academy Editions.

To cite this article: Saligheh, E., & Badri Benam, N. (2019). Dome on squinches: An innovation in construction technology of ancient Iran. Online Journal of Engineering Sciences and Technologies, 2(1), 1-4.

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