The Church of Hagia Sophia was built in the 6th century under Emperor Justinian I. It is located at the intersection of the two main roads in Iznik that connect the four gates. Built to serve as the principal place of worship in Byzantine Nicaea (Iznik), the church housed the 7th Ecumenical Council in 787. In 1065, and earthquake destroyed Hagia Sophia and a new church was built in its place which has come to our day. The Ottomans converted the church into a Friday mosque right after they conquered the city in 1331. A madrasa (medrese) and baths (hamam) were built near the Orhan mosque, as it came to be called after the Conqueror Sultan. A fire in the mid 15th century gutted the building that was spoiled in 1402 by the Mongol raids. At a time when Iznik was revived with the introduction of faience manufacture, the building was renovated by Mimar Sinan following the order of Süleyman I (1520-1566). The mosque fell in disrepair two centuries later as Iznik lost its prosperity, and was abandoned when the roof collapsed.

The church-mosque is based on a basilica plan and consists of a nave that extends west to east, flanked by aisles to the north and south. Today the structure of the walls remains intact, while the roofs of the nave and the aisles have collapsed. The three apses terminating the nave and the aisles have survived with their domes. The semicircular central apse projects on the exterior while the side apses are rectangular spaces closed in to form rooms where remains of painted decorations are still seen around the windows.

At the time of conversion, a new wall with mihrab niche was built at an angle to the southern apse to mark the qibla direction. Only the base remains of the minaret that was added at the northwest corner of the church-mosque. Renovations planned by Mimar Sinan in 16th C., on the other hand, have involved architectural interventions to the original structure. The access from the aisles to the nave, provided previously by two sets of three narrow archways, was modified to create a larger open space by removing the columns and combining the arches to form two wide archways on both sides. At this time too, the interior was covered with Iznik tiles.

The Hagia Sophia has been a museum since the early Republican years. Archaeological excavations on the site in 1935 and 1953 have cleared the interior of dirt, revealing the colored floor mosaics and the sythronon of the central apse. In recent digs, the area around the building has been excavated, lowering the ground level to 2.5m below the current level in order to reveal the exterior of the walls. The windows are currently filled in to limit access to the interior. Nothing remains of the madrasa or the baths that were built in the vicinity of the church-mosque in 1331.

Sources:

Iznik. Tarih ve Müze Komitesi Yayini, Kenan Matbaasi: Istanbul, 1943
Türkiye'de Vakif Abideler ve Eski Eserler. (Volume IV) Vakiflar Genel Müdürlügü Yayinlari: Ankara, 1972.

Aru, Kemal Ahmet. Türk hamamlari etüdü. Istanbul Matbaacilik: Istanbul, 1949.

Ayverdi, Ekrem Hakki. Osmanli mi'marisinin ilk devri: Ertugrul, Osman, Orhan Gaaziler, Hüdavendigar ve Yildirim Bayezid 630-805 (1230-1402): I. Baha Matbaasi: Istanbul, 1966.

Eyice, Semavi. Iznik: Tarihçesi ve Eski Eserleri (Nicaea: The History and the Monuments). Sanat Tarihi Arastirmalari Dergisi Yayinlari: Istanbul, 1988.

Taylor, Jane. Imperial Istanbul : a traveler's guide, includes Iznik, Bursa and Edirne. I.B. Tauris Publishers: London, 1998 (revised edition).

Yalman, Bedri. Iznik (Nicaea). Governorship of Bursa, Provincial Directorate of Tourism: Bursa, 1999