The Hagia Sophia that you can visit today was the primary church of Byzantine Constantinople and was built upon the site of two earlier churches that had been destroyed. Emperor Justinian I (527-565) commissioned the project and had materials brought in from all around his empire for the massive church’s construction. The Hagia Sophia was the most important church of the Christian East. Structurally, it was the first of its design and boasted the largest dome that had yet been engineered which provided a voluminous and well illuminated interior. After Constantinople fell to the Ottomans in 1453, the Hagia Sophia was converted into a mosque and was used as such throughout the Ottoman period.