Nan Madol, Archaeological ruins in Madolenihmw, Federated States of Micronesia

Nan Madol is a complex of ruins on artificial islands in Madolenihmw, Pohnpei, connected by a network of waterways. Tall walls of stacked basalt columns form residential areas, tombs, and ceremonial platforms above the tidal waters of the lagoon.

Human activity at the site dates to the 1st or 2nd century AD, and islet construction began by the 8th or 9th century. Megalithic building with large basalt stones started around 1180–1200, when Nan Madol became the seat of the Saudeleur dynasty. Around 1628 Isokelekel overthrew the Saudeleurs; his successors abandoned the site.

The name Nan Madol means "within the intervals", after the tidal canals that crisscross the ruins; an older name, Soun Nan-leng, means "Reef of Heaven". Pohnpeian tradition credits twin sorcerers, Olisihpa and Olosohpa, with raising the stones by levitation, and the site is also called the "Venice of the Pacific".

Tidal currents can make navigating the canals challenging, so hiring an experienced local guide is helpful. Some areas flood at high tide while others are best explored at low water levels.

The basalt columns were transported from Pohnpei Island across several kilometers without using wheels or draft animals. Some stone blocks weigh up to 50 tons and were precisely stacked without mortar or binding agents.