Abstract
Over the centuries, Iranian architects have created magnificent masterpieces of architectural works. One of the most substantial structural components of a building in Iranian indigenous architecture, which significantly influences the formation and durability of the architectural work, is the coverings, especially domes and arches. A notable point about the dome-shaped architectural forms is the static nature of these traditional structures. The Sassanian era is significant for Iranians, with many analyses discussing its building structures. At the beginning of the Sassanian Empire, when Zoroastrianism was declared the official religion, Zoroastrian fire temples were found to be a stable stronghold for their rule. In Zoroastrianism, the four essential elements (water, fire, air, and earth) are regarded as sacred, and contaminating them is considered sinful. Among these, fire was given the most importance because, besides being pure and sacred, they benefited from its light and warmth. For this reason, during the Sassanian period, besides constructing significant and large fire temples, many chahartaqs were also built where religious ceremonies were held.
On the other hand, Iranian architects have traditionally used the dome in buildings as a symbol of the sky and a means of connection between earth and God, and they were even the first people to present creative ways of constructing this element on a square base. They have extensively used this identity-forming element in structures such as mosques and mausoleums. Since then, Iranian architects have created various types of domes with the best form and shape using traditional methods. Sassanian architects had great skill in erecting arch and dome coverings on a square base, and their method of erecting domes spread and continued in various regions. During the Sassanian period, dome construction became so prevalent and evolved that since then, the dome covering has been used as a general pattern and guideline for construction and durability. However, traditional architects designed the functional properties of the building elements in religious structures so that their hidden meanings would be revealed.
General studies on well-known religious buildings of the Sassanian period show that religious buildings of this era often have a chahartaq plan. One of the important issues in the construction of arches and domes is the method of construction and the stability of these structures. The present research is applied in terms of purpose. The research method is qualitative, and the analysis method is descriptive, in such a way that using the cognitive background and the results obtained from field research and collecting information and documentary studies, it seeks to achieve the development of applied knowledge and achieve a practical goal. The main objective of this research is to produce knowledge and awareness in examining various dome and arch structures in the Sassanian period and the methods of construction and stability. In this study, first, by collecting findings and scientific documents, the construction methods of dome and arch structures are studied, and finally, the statics and stability of these structures are examined and analyzed. Ultimately, using observations, field surveys, maps, and existing documents, we examine the materials, construction methods, and statics of the SIAHGEL fire temple. TThe research findings indicate that the structural stability of the SIAHGEL fire temple is attributed to the use of durable materials like stone, lime, plaster, and sarooj mortar, along with construction methods like chahartaq and the incorporation of porticoes around the dome, as well as the distribution of forces onto four pillars. On the other hand, identifying Sassanian chahartaqs and associating them with the Sassanian era and the utilization of fire temples poses a challenge when studying religious structures from this time. Before this, any chahartaq identified with mortar, rubble stone, and sarooj was attributed to the Sassanian period, but perhaps a more careful examination could reveal that the construction of buildings in this style continued even in the early Islamic period. The Sassanian chahartaqs, known as fire temples, have a circumambulation hall around the building and also benefit from a central hall with the fire temple located in the central hall, which the examined example, the SIAHGEL fire temple, has all these characteristics that are specific to the buildings of the Sassanian period.
Besides the wide variety of materials used in this period (rubble stone, cut stone, brick, mud brick, clay, mud, plaster, wood, etc.), the masterful use of rubble stone and plaster mortar for constructing various buildings is a distinctive feature of the architecture of this period. About the SIAHGEL fire temple, we can say that the use of durable materials such as rubble stone, sarooj, and plaster mortar, as well as the masterful application of large arches (porticoes) around the dome chamber, are among the reasons for the structural stability of this chahartaq building.