The Koursum Tzami is the only surviving mosque of the seven in the city and together with the Madrrassa and the Ottoman Barracks it is one of the most important monuments of the architectural heritage of the Ottoman period. It is located in today’s Alexandrou Square of Kastoria. Its exact date remains unknown, but it is likely that it is a mosque of Mehmet (Mehmet II) and in combination with its architectural and morphological elements it is likely to date back to the 15th century.
Architecturally it follows the type of provincial Ottoman mosques of the Balkans. It is a one-roomed, cubic-shaped building with external dimensions of approximately 10 x 10 m. The entrance was originally located on the north-western side, where it had a revak. It is covered by a hemispherical dome and consists of the main prayer room decorated with muqarnas and the minaret in the north-western corner. Inside, there are remains of the prayer niche (mihrab), traces of the wooden construction of the pulpit (minbar) and embedding spots of the wooden balcony (dikka). From time to time, repairs and changes were made to the monument, such as replacing the lead covering of the dome with tiles and converting a window into a doorway. During the Second World War, the monument was used as a rations preparation area then as a library and in recent years as a storage area by the Archaeological Service. Restoration and maintenance work has been started on the monument by the Ephorate of Antiquities of Kastoria with the funding of the Recovery Fund.