Nan Madol is a series of more than 100 artificial islets in a lagoon off the south-east coast of Pohnpei. On these islets are the remains of stone palaces, temples, tombs and residential domains built between 1200 and 1500 CE. These ruins represent the ceremonial centre of the Saudeleur dynasty, a vibrant period in Pacific Island culture. The huge scale of the edifices, their technical sophistication and the concentration of megalithic structures bear testimony to complex social and religious practices of the island societies of the period. Steps are being taken to counter threats from vegetation overgrowth and storm surge.