stylistic:tone, linguistic:voice_change, structural:reformatting
Renovation of 1847–1849

The 19th-century restoration of the Hagia Sophia was ordered by Sultan Abdulmejid I (r. 1823–1861) and completed between 1847 and 1849 by eight hundred workers under the supervision of the Swiss-Italian architect brothers Gaspare and Giuseppe Fossati. The brothers consolidated the dome with a restraining iron chain and strengthened the vaults, straightened the columns, and revised the decoration of the exterior and the interior of the building. The mosaics in the upper gallery were exposed and cleaned, although many were recovered "for protection against further damage".

Eight new gigantic circular-framed discs or medallions were hung from the cornice, on each of the four piers and at either side of the apse and the west doors. These were designed by the calligrapher Kazasker Mustafa Izzet Efendi (1801–1877) and painted with the names of Allah, Muhammad, the Rashidun (the first four caliphs: Abu Bakr, Umar, Uthman and Ali), and the two grandsons of Muhammad: Hasan and Husayn, the sons of Ali. In 1850, the architects Fossati built a new maqsura or caliphal loge in Neo-Byzantine columns and an Ottoman–Rococo style marble grille connecting to the royal pavilion behind the mosque. The new maqsura was built at the extreme east end of the northern aisle, next to the north-eastern pier. The existing maqsura in the apse, near the mihrab, was demolished. A new entrance was constructed for the sultan: the Hünkar Mahfili. The Fossati brothers also renovated the minbar and mihrab.

Outside the main building, the minarets were repaired and altered so that they were of equal height. A clock building, the Muvakkithane, was built by the Fossatis for use by the muwaqqit (the mosque timekeeper), and a new madrasa (Islamic school) was constructed. The Kasr-ı Hümayun was also built under their direction. When the restoration was finished, the mosque was re-opened with a ceremony on 13 July 1849. An edition of lithographs from drawings made during the Fossatis' work on Hagia Sophia was published in London in 1852, entitled: Aya Sophia of Constantinople as Recently Restored by Order of H.M. The Sultan Abdulmedjid.