Siege of Tripoli ( 1551 ) The Siege of Tripoli occurred in 1551 when the Ottomans besieged and vanquished the Knights of Malta in the fortress of Tripoli , modern Libya . The Spanish Habsburgs had established a fort in Tripoli in 1510 under Charles V , and remitted it the Knights in 1530 . The siege culminated in a six - day bombardment and the surrender of the city on 15 August . The siege of Tripoli succeeded an earlier attack on Malta in July , which was repelled , and the successful invasion of Gozo , in which 5 , 000 Christians captives were taken and brought on galleys to the location of Tripoli . Siege . The city was under the command of Father Gaspard de Vallier , with 30 knights ( some authors say 200 ) and 630 Calabrian and Sicilian mercenaries . The Ottomans had a base since 1531 in the city of Tajura , 20 kilometers to the east , where Khayr al - Din had been based . The Ottomans encircled the fort , and established 3 batteries of 12 guns each . The French Ambassador to the Ottoman Empire , Gabriel d ' Aramon , joined the Ottoman fleet at Tripoli , with two galley s and a galliot , The declared mission of the ambassador was to dissuade the Ottomans from capturing the city , at the request of the Grand Master of Malta , as Malta was not identified as an enemy in the Franco - Ottoman alliance against the Habsburgs . According to later reports , when Sinan Pasha and Dragut refused to lift the siege , on grounds that they were under order to eradicate the Knights of Malta from the African continent , d ' Aramon threatened to sail to Constantinople to appeal to Suleiman , but he was then barred from leaving the city until the end of the siege . Soon the soldiers in the fort mutinied , and negotiation for surrender started . The city was captured on 15 August 1551 by Sinan Pasha after six days of bombardment . The Knights , many of them French , were returned to Malta upon the intervention of the French ambassador , and shipped onboard his galleys , while the mercenaries were enslaved . Murād Agha , the Ottoman commander of Tajura since 1536 , was named as the " Pashalik " of the city . Nicolas de Villegagnon , the future explorer of Brazil , was present at the siege of Tripoli in 1551 , and wrote an account about it in 1553 . Aftermath . From Malta , d ' Aramon wrote a letter about his intervention to Henry II . The role of d ' Aramon was widely criticized by Charles V and Julius III on suspicion that he had encouraged the Ottoman to take the city . It appeared that d ' Aramon had participated to the victory banquet of the Ottomans , raising further suspicion on his role in the siege , and leading to claims by Charles V that France has participated to the siege . In any instance , d ' Aramon had a special relationship with the Ottomans , and was clearly aware that the fall of Tripoli represented a major setback for Charles V . Upon his return to Malta , Gaspard de Vallier was heavily criticized by the Grand Master D ' Omedes who wished to assign all the blame for the defeat on him . He was brought in front of a tribunal , and stripped from the habit and cross of the Order . He had been however staunchly defended by Nicolas de Villegagnon , who exposed the duplicity of D ' Omedes . The siege was the first step of the all - out Italian War of 1551 – 1559 in the European theater , and in the Mediterranean the French galleys of Marseilles were ordered to join the Ottoman fleet . In 1553 , Dragut was nominated commander of Tripoli by Suleiman , making the city an important center for piratical raids in the Mediterranean and the capital of the Ottoman province of Tripolitania . In a famous attack from Tripoli , in 1558 , Dragut attacked Reggio , and took all its inhabitants as slaves to Tripoli . In 1560 , a powerful naval force was sent to recapture Tripoli , but that force was defeated in the Battle of Djerba .