In 554 A.D. one of the most terrible earthquakes ever occurred. The earth shook for 14 days and is well documented by the historian Agathias who happened to be in Kos at the time.
The frightening tremors and explosions made the earth subside and the sea rushed in and ravished the coastline taking with it people, buildings and anything else in its way. In 1306 A.D. kalymnos is conquered by the Knights of the Order of Saint John from Jerusalem. The order has Rhodes as it's administrative capital which it managed to subdue after three years of resistance by the Rhodians.