# Structural Detection and Restoration Proposal for the Mardin Sahkulubey Cupola
## 1 Introduction
Research on the historical Ankara Castle contributed significantly to the restoration by concluding that granite was used on the eastern facade of the forwtes walls, andestie on the southern facade, and baked clay products on the northern and western facades [16]. During the restoration works for the Kutahya Castle, it was observed that the stones used in the walls of the Kutahya Castle had different compressive strength values. Thus, it is suggested that the section to be restored should account for differences in the quality and aging of the stones during the integration and strengthening techniques. As a result of the S.E.M. analysis, the images obtained at \(\times\)50, \(\times\)100, \(\times\)250, \(\times\)500, \(\times\)1000, and \(\times\)2000 magnifications were consistent with the results of the physical experiments. In the E.D.S. analysis, it was determined that the samples showed calcium oxide (CaO), that is, limestone and calcium aluminate (CaAl\({}_{2}\)O\({}_{3}\)) properties, according to the information given in the geological maps of the region [17]. In masonry structures, the mortar that binds the material is as important as the carrier material. In this context, in a study on Roman, Byzantine, and Seljuk period mortars, the mortars' physical, chemical, mechanical, and microstructural properties were investigated. Although the structures were built in different periods, the material properties (physical, chemical, and mechanical) obtained as a result of the analyses showed similarity when compared across periods, since the mortar material was obtained from the sources in the region and rocks with similar characteristics [18]. In a study on the Emir Saltuk Cupola, a photogrammetric survey was prepared for the Emir Saltuk Vault, one of the three vaults in Erzurum. In addition, three-dimensional point data were created by measuring control points using a total station. Surveys were prepared to serve as a basis for the restoration projects [19]. In a study on the Kemah Grave Monuments, nine mausoleums (vaults and tombs) located in the Kemah district of Erzincan province were examined in terms of plan, architecture, and decoration. In addition, the place and importance of the works in Anatolian Turkish-Islamic architecture were emphasized [20]. In the research on the restoration of the Akseki Buttoned Houses, as a result of S.E.M. analysis, the images obtained at \(\times\)50, \(\times\)100, \(\times\)250, \(\times\)500, \(\times\)1000, and \(\times\)2000 magnificationswere compatible with the results of the physical experiments. In the E.D.S. analysis, it was determined that the samples showed calcium oxide (CaO), that is, limestone and calcium aluminate (CaAl\({}_{2}\)O\({}_{3}\)) properties, according to the information given in the geological maps of the region [21]. No previous studies in the literature focused on the construction technique of the Sahkulubey Cupola. There are only limited observations that are not in-depth, and these observations indicate that there was no floor in the crypt, the dome was built on an octagonal structure, and the material utilized was cut stone. This study determined the characterization of the materials used in the construction of the Sahkulubey Cupola. It aimed to obtain essential findings that will shed light on the selection of materials for restoration works. The Mardin stone examined within the scope of this study is frequently seen and used in the Mardin-Kizlitepe-Omerli-Midyat regions. Mardin stone was deposited during the Lower Eocene-Lower Oligocene reef-origin Hoya Formation. The average thickness of the formation is between 50 and 600 m. The lithologies that form the formation are chalky limestones, biomimetic, dolomitic limestones, clayey limestones, and fossiliferous limestones. The colors of our rocks are yellow, pink, red, white, off-white, gray. The formation was formed on the shallow sea-shelf edge and occasionally presents products with reef characteristics.