In 1521 , Philippe Villiers de L'Isle-Adam was elected Grand Master of the Order . Expecting a new Ottoman attack on Rhodes , he continued to strengthen the city 's fortifications , work that had begun after the Ottoman invasion of 1480 and the earthquake of 1481 , and called upon the Order 's knights elsewhere in Europe to come to the island 's defence . The rest of Europe ignored his request for assistance , but Sir John Rawson , Prior of the Order 's Irish House , came alone . The city was protected by two and , in some places three , rings of stone walls and several large bastions . The defence of the walls and bastions was assigned in sections to the different '' Langues '' into which the knights had been organized since 1301 . The harbour entrance was blocked by a heavy iron chain , behind which the Order 's fleet was anchored
earthquake of 1481
1481 Rhodes earthquake
Siege of Rhodes (1522)