International audienceThis essay is a largely redesigned version of an article published in Turkish in 2015 in Istanbul. The purpose of this one was to draw the attention of Turkish officials to the urgent need to safeguard the only, very precious but critically endangered, element of the Xckōnk‘ [Khətzkonq] monastic complex, St. Sergius Church. Built in 1024, this tetraconch, inscribed in a quasi-rotunda, is adorned with an elegant blind colonnade-arcade, characteristic of the Ani school, and is topped with a pleated umbrella dome, called "brilliant crown" by the chronicler of the 12th c. Samuel of Ani. The article attempts to examine the origin and the manifestations, through centuries and traditions, of this structure, remarkable creatio...