attack on the Cittadella took place in July 1551, when a large Ottoman force, led by admiral Sinan Pasha, invaded Gozo and besieged the Cittadella. Governor Gelatian de Sessa offered terms of surrender, but they were refused, and the castle fell within a matter of days. The castle was then sacked, and most of the 6,000 Gozitans, who took refuge there, were taken as slaves. The attack left the castle in ruins, but it was rebuilt soon afterwards, although, initially, no efforts were made to modernize it. The Cittadella was undamaged during the Great Siege of Malta in 1565. Although there had been proposals to demolish the castle and evacuate its inhabitants to Sicily, the castle served an important role during the siege, as it maintained a communication link between besieged Birgu and Christian vessels, and it also reported Ottoman movements to the Order. After the siege, Grand Master Jean Parisot de Valette and military engineer Francesco Laparelli visited the Cittadella in order to modernize it, but nothing materialized since at the time the Order was busy constructing its new capital Valletta on mainland Malta. The Cittadella was attacked again by corsairs in 1583. In 1599, a major reconstruction of the Cittadella begun, under designs of the military engineer Giovanni Rinaldini and under the direction of Vittorio Cassar. The southern walls of the city were completely rebuilt as a bastioned enceinte with a single bastion and two demi-bastions linked by curtain walls, along with two cavaliers, a ditch and outworks. Parts of the northern walls were also rebuilt by the Hospitallers, although they retained a medieval form. The walls surrounding the suburb Rabat were probably demolished at this point. The reconstruction to Rinaldini's and Cassar's designs was completed in around 1622. Gozo's population stayed within the walls of the Cittadella between dusk and dawn until this curfew was lifted on 15 April 1637. The castle remained the only fortified refuge against attack for the island's inhabitants until Fort Chambray was built in the mid-18th century. Soon after the reconstruction was complete, the Cittadella's defences were again criticized. In the 1640s, plans were made to demolish the citadel and build a new fortress at Marsalforn. Mines were actually built under the bastions to destroy them, if necessary, but the demolition was never done. The engineer Antonio Maurizio Valperga suggested to rebuild the wall around the suburb and further strengthen the Cittadella,