 Nan Madol, a UNESCO World Heritage site, consisting of a series of small artificial islands linked by a network of canals, is often called the Venice of the Pacific.It is located on the eastern periphery of the island of Pohnpei and used to be the ceremonial and political seat of the Saudeleur dynasty that united Pohnpei's estimated 25,000 people from about AD 500 until 1500, when the centralized system collapsed.European explorers—first the Portuguese in search of the Spice Islands (Indonesia) and then the Spanish—reached the Carolines in the sixteenth century.