Restoration of the Hagia Sophia was ordered by Sultan Abdulmejid I (r. 1823–1861) and completed by eight hundred workers between 1847 and 1849, 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.[101] The mosaics in the upper gallery were exposed and cleaned, although many were recovered "for protection against further damage". [citation needed]