 Complete the following phrase:  Emperor Charles V handed over Malta and Gozo to the Order of St. John in 1530. The Order was in a state of perpetual war against the Ottoman Empire, which had expelled it from its previous base at Rhodes in 1522. At the time the Cittadella was still a medieval castle, and it provided refuge for the Gozitans during Ottoman or Barbary attacks. The largest attack on the Cittadella took place in July 1551, when a large Ottoman force, led by admiral Si Pasha, 