The Hagia Sophia of Nicæa is a historic church located in the city of Nicæa, now known as İznik in modern-day Turkey. Built in the early 6th century during the reign of the Byzantine Emperor Justinian I, it served as a significant center for Christianity and was the site of the Second Ecumenical Council in 787 AD. This architectural marvel features a large dome and intricate mosaics, showcasing the artistic achievements of the Byzantine era. The church was later converted into a mosque after the Ottoman conquest, reflecting the region's diverse religious history. Today, it stands as a symbol of cultural heritage.