Hasankeyf historic settlement area is one the most important sites in southeastern Anatolia which dates back to the 15th century. Zeynelbey Tomb is a distinct cylindrical structure has a height of 9.6 m and with double domes extending to an overall height of 16.5m; however, the outer dome suffers from multiple and large vertical tension cracks threatening the overall structural stability and safety of the structure. A preliminary visual inspection and structural evaluation using analytical modeling was carried out. The tension zones developing at the outer dome was determined using analytical simulations and causes of vertical tension cracks were elaborated. A general remedy of strengthening was developed to surround the dome using vertical ribs and horizontal post tensioning strands that are placed in three vertical layers. The deterministic analytical simulations using the horizontal post-tensioning have allowed finding the necessary amount of tension force in each horizontal strand to diminish the tensile stresses inside the dome and put the structure in a stable compression state. This paper describes the steps carried out for the assessment, evaluation, and retrofit studies, which might set an example to similar historic structures with comparable structural problems in the dome.