The Types and Usage of Building materials in the West Iwan of Takht-e Soleymān

The western iwan of the Takht-e Soleymān is one of the most important buildings in this area. Based on some accounts, this iwan was constructed during the Sāssānid period and the Ilkhanate kings restored it after 700 years. This unique structure is statically unstable and needs strengthening. To this end, becoming familiar with the building materials and their use in this structure are important. The aim of this research is examining the building materials used in the western iwan of Takht-e Soleymān in the two significant architectural periods of Takht-e Soleymān (Sāssānid and Ilkhānid), with focus on the use of the building materials and their positioning. This research has been conducted using the field study method. The research results show that the building materials used in the construction of the western iwan are stone, brick, and half baked, half worked plaster. Smoothed stone is used in the first architectural period following the style of all the other structures built in the area. Using the excavations near the iwan abutment, and comparing with the northern and sudden supports, it was revealed that the abutment of the iwan are rows of smoothed stone in stretcher bond formation. The main body of the abutment, up to the brickwork, is also built from smoothed stone to a height of 5.2 meters. The remarkable point in this regard is the gradual change of the stretcher brickwork to the stretcher-header brickwork (similar to the method used in the perimeter wall). This is done in such a way that the lower rows are stretcher brickwork and the higher rows are stretcher header. On the top part and the top of the smoothed masonry, square bricks are used with sides of 29 centimetres and thickness of 7 centimetres. The brickwork is stretcher with a one third overlap. By observing the similar buildings to the iwan in the area, it seems that the barrel vault was also made of bricks. The mortar used in the construction of stone and brick part in this architectural period was half baked, half worked plaster. In the second architectural period in which the Ilkhanate reconstructed the parts fallen down since the first architectural period, stone rubble and plaster were the main building materials. The top parts and some of the parts which had been separated from the body of the iwan as a whole layer were reconstructed. A cover of ornamental tiles [qashani] and from the inside and muqarnas in the apex of the iwan. The stone rubble used in the western iwan in this period was the remnants of the building materials used in the first period which differed in dimension and was placed in horizontal rows. The impost of the vault is evident by a 10 cm projection of the building materials. The mortar used is half baked half worked plaster as was revealed using chemical analysis. Another remarkable element in this period is the qashani covering the inside of the abutments which is a remarkable ornamental element of the Ilkhanate period in this location. The eastern front and the sides of the iwan entrance, there are remnants of plaster muqarnas in three rows.