The Fossati brothers, Gaspare (7 October 1809 — 5 September 1883) and Giuseppe (1822-1891), were Swiss-Italian architects. They completed more than 50 projects in Turkey during the Tanzimat era. They belonged to the Morcote branch of the Fossati, a prominent Ticinese family with mentions in the historical record going back to the 14th century.
Born in Ticino, they finished primary and middle school in Venice and studied architecture at the Brera Academy in Milan. At the end of 1836, Gaspare was appointed to Istanbul for the project of building in the Russian Embassy.
Between 1841 and 1843, the Fossati brothers built the brick Bab-ı Seraskeri Hospital (Bekirağa Bölüğü) and Liman İskelesi Karakolu in Eminönü for the Ottoman Administration. They were appointed to renovate Arzuodası at Babıali in 1844, and to build important buildings in Sultanahmet such as Dârülfünun (university) (1845-1846), Hazine-i Evrak, and Mekteb-i Sanayi (1846-1848).
In 1847, Sultan Abdülmecid appointed them to renovate the Hagia Sophia. They completed the restoration in two years, utilizing more than eight hundred workers. They were able to document a larger number of Byzantine mosaics whose precise location within the Hagia Sophia today have not been fully documented since many were either painted over or destroyed often without recording their original location. The drawings of the Hagia Sophia mosaics are kept in the Cantonal Archive of Ticino. Sultan Abdülmecid allowed the brothers to also document any mosaics they might discover during this process which were later archived in Swiss libraries.
The Telgrafhane-i Amire building was built by Giuseppe Fossati in 1855. Upon the death of Reşit Paşa in 1858, the Fossati brothers built his mausoleum in the corner of the graveyard in the Bayezit complex.