This text is a fragment of a guidebook to Iznik "The Highlights of Iznik. Treasures of the ancient Nicaea".

A small and quite inconspicuous building of the historical Hagia Sophia church is located in the centre of Iznik. For many centuries, it has been a silent witness to important events that have had a significant impact on the fate of large human communities, sparked heated debates and stirred up huge controversies. Even in the 21st century, the political decisions made about its future caused a media storm and provoked discussion about the direction in which The Republic of Turkey is heading.

In the 6th century CE, Justinian I, the Roman emperor from 527 to 565, decided to build the Church of the Holy Wisdom in Nicaea. It was the second church of this name erected during his reign - the first was the famous Hagia Sophia in Constantinople. The Hagia Sophia in Nicaea was constructed on the plan of a rectangular basilica. The main nave runs from east to west, and on both sides are side naves. All naves end with semicircular apses and are covered with domes.

In 787 CE, The Second Council of Nicaea was held in the local Hagia Sophia church. It was the last of the first seven ecumenical councils, recognised by both the Eastern Orthodox Church and the Roman Catholic Church. During this Council, the Christian bishops mainly debated the issue of iconoclasm, or the ban on the worship of images by the Christians. The Council determined that the honorary veneration of icons was permitted, but the true adoration was reserved for the God alone.

In 1065, the Hagia Sophia church in Nicaea was destroyed by an earthquake and then rebuilt in a form similar to the one seen today. After the conquest of Nicaea by the Turks in 1331, the Hagia Sophia was transformed into the Orhan Mosque (tr. Orhan Camii), named after the victorious sultan. A madrasa and baths were built next to the mosque.

Unfortunately, soon, in 1402, the building was seriously damaged during the Mongol invasions, and the destruction was completed by a fire in the mid-15th century. For about one hundred years, Hagia Sophia in Nicaea was a ruin. It was only the revival that Iznik experienced due to the development of faïence factories that sparked renewed interest in the fate of the building.

On the orders of Sultan Suleiman the Magnificent, who ruled from 1520 to 1566, the renowned Ottoman architect Sinan took up the renovation of the mosque. The interior of the building was reconstructed to better serve the function of a mosque and covered with famous local tiles, and a minaret was built on the north-west side.

For two centuries, Hagia Sophia functioned as a mosque, before falling into ruin again when Iznik lost its importance as a centre of ceramic production in the 18th century. In 1920, the building was badly damaged by a fire during the Turkish-Greek War. Since then, for over 80 years, Hagia Sophia was open to tourists as a museum, although in a deplorable state.

In 1935 and 1953, archaeological excavations were carried out on the Hagia Sophia's site, during which the interior of the building was cleared, revealing the colourful floor mosaics. As a result of the excavations, the ground around the building sank by 2.5 metres, revealing the external walls. However, there are no traces of the 14th-century madrasa and baths today.

In 2007, a major renovation of the building was completed. The process included rebuilding the minaret, roof, and dome, laying a new floor covered with carpets, installing a pulpit and a sound system. A ticket sales booth was placed in front of the entrance. On November 6, 2011, the first day of the Feast of the Presentation (tr. Kurban Bayramı), the Hagia Sophia was officially opened as the Ayasofya Mosque.

This decision, made by the General Board of Religious Endowments, caused a huge outcry among conservators, Christian organizations, and tourists. Even some Muslim residents of Iznik spoke out against the move, arguing that there were enough mosques in the city. However, Adnan Ertem, director of the Orhan Gazi Foundation, said the building had been used as a mosque for 680 years and had never been officially converted into a museum, so there was no obstacle to its restoration as a mosque.

At the beginning of 2025, Pope Francis announced that he will visit Iznik and its Hagia Sophia in May 2025, to mark the 1700th anniversary of the First Council of Nicaea which was held in the city in 325. This Council was, most probably, held in the church found under Lake Iznik several years ago.

Today, Hagia Sophia functions as a mosque and no entry fees are collected from the visitors. It is necessary to remember to dress appropriately and avoid visiting during Muslim prayer times.