In 1847, Sultan Abdulmejid (1839-1861) wished to renovate the Hagia Sophia and specifically summoned the Italian-Swiss Gaspare Fossati (1809-1883), "Court Architect" in Saint Petersburg, who had extensive experience from the excavations of Pompeii, Poseidonia (Paestum), and other Italian necropolises.

Gaspare, along with his brother Giuseppe, completed the work in two years, employing over eight hundred workers. The cracked domes were repaired, iron chains were placed at their bases for reinforcement, and the famous mosaics, which had been covered with plaster since the time of Mehmet II, were cleaned and restored.

Gaspare Fossati added architectural elements (such as the sultan's throne, which was protected by a gilded lattice) by combining Turkish Rococo with Byzantine colonnades. The restoration works were captured in colorful watercolors and published in 1852 in London in an album titled "Aya Sophia of Constantinople as Recently Restored by Order of H.M. The Sultan Abdulmedji."