In the middle of the Pacific Ocean, between the equator and the eleventh parallel, lies the city of Nan Madol on the island of Pohnpei. Considered to be one of the greatest archeological wonders of the world, it is the only ancient city ever built atop a coral reef, and, like Easter Island, it is an engineering marvel.

Nan Madol, part of the Federated States of Micronesia, is comprised of a vast tapestry of 92 artificial islets all interconnected by canals. The megalithic structures were constructed primarily with basalt logs, a volcanic rock that…