The first great masterpiece of Byzantine architecture, the Hagia Sophia — "Holy Wisdom" — perfected the use of an architectural element called the pendentive, which allowed a round dome to be placed above a square room. The row of arches at the base of the dome allowed light to enter the structure, creating its distinctive luminous interior.
The Emperor Justinian built the Hagia Sophia as an Orthodox Christian church. During the Latin Occupation of Constantinople, it became a Roman Catholic church, and since 1453 has been a mosque. It has been restored and refurbished several times after damage from earthquakes.