Bana cathedral

Bana is a ruined early medieval cathedral in present-day Erzurum Province, eastern Turkey, in what had formerly been a historical marchland known to Armenians as Tayk and to Georgians as Tao.

It is a large tetraconch design, surrounded by a near-rotunda polygonal ambulatory and marked with a cylindrical drum. Generally believed to have been constructed in the 7th century, based on an 11th-century chronicle it was reconstructed by Adarnase IV of Iberia at some point between 881 and 923. Henceforth, it was used as a royal cathedral by the Bagrationi dynasty until the Ottoman conquest of the area in the 16th century. The former cathedral was converted into a fortress by the Ottoman army during the Crimean War. The monastery was almost completely ruined during the Russo-Turkish war of 1877–78.

Source: Wikipedia