Today Nan Madol forms an archaeological district covering more than 18 km² and includes the stone architecture built up on a coral reef flat along the shore of Temwen Island, several other artificial islets, and the adjacent Pohnpei main island coastline.
Carbon dating indicates that megalithic construction at Nan Madol began around 1180 AD when large basalt stones were taken from a volcanic plug on the opposite side of Pohnpei.