The fort was built by the Order of Saint John after the 1551 attack, on the peninsula then known as Isola di San Michele formed by Dockyard Creek and French Creek in Grand Harbour. The fortified city of Senglea which was later built around the fort is still known locally as l-Isla. The original fort was begun in 1551, initially under the patronage of Grand Master Juan d'Homedes, to a design by the military engineer Pedro Pardo d’Andrera, and extended to a fortified city by Grand Master Claude de la Sengle during the Knights' preparations for the Siege of Malta.