Qasr-e Shirin owes its prominence primarily to the Sassanian period and the attention the region received from Khosrow Parviz. Khosrow took the first steps to make Qasr-e-Shirin habitable by constructing a complex consisting of a palace, a fortress, a religious building, a defensive wall and a water conveyance system. Later, Qasr-e-Shirin is mentioned in several texts and travel itineraries. The Char-Ghapi complex is generally attributed to the Sassanian king Khosrow II (590-628 A.D.), who allegedly constructed it for her Christian wife Shirin, thus the name Qasr-e-Shirin. Some historical sources make allusions to the buildings in Qasr-e-Shirin (Khosrow’s Mansion, Char-Ghapi). Char-Ghapi of Qasr-e-Shirin has a square ground plan with domed roof, known as chahar-taghi, which has attracted attention from many scholars, who have described it as a structure from the late Sassanian period. The majority of scholars have characterized its chahar-taq or square dome as a fire temple, while some have claimed that it formed part of a palace complex; a few writers have also expressed doubts as to its chronology, suggesting a date in the early Islamic period for it. Therefore, the most important questions about this structure concern its construction date and function. In view of its architectural style, its comparison to the plan of the historical temples, and the political history of the Sassanians, the Char-Ghapi complex might have had a religious function; then, by studying the Christianity in Iran in particular in the late Sassanian period, one may conjecture that Char-Ghapi was probably a church that was never completed. The Sassanian complex in Qasr-e-Shirin was probably partially destroyed during Heraclius’ Persian campaign of 628 A.D., which also might have brought a permanent halt to the construction operation there and Qasr-e-Shirin never gained its previous fame again though the name survived as a small village as late as the Qajar period. Several structures lying on the east of the square dome, not to mention its structural differences with the standard fire temple plan, are what cast the most doubt on the idea that Char-Ghapi was a fire temple. Since the meaning of a given building is determined by its similarity to other related structures, the present work aimed to determine the true nature of Char-Ghapi through drawing comparisons with other contemporary structures.