Built on the southeastern end of Pohnpei, they were constructed over a period of 1000 years, from 500 AD to the mid 1500's. These prisms were brought in from quarries located at various places around the island with coral rubble being used as fill for the islets' floors. This type of architecture occurs only sporadically on the main island which suggests that the people who used these structures were of very high status. It is not known whether the original builders considered the advantage of a high thermal mass assembly cooled through conductivity and evaporation via the surrounding ocean water, when they chose this method of construction. They were probably more concerned with durability and defense.
Today there is an understanding of the concept of cooling through the use of shaded thermal mass.
Some of the people I met considered concrete construction to be one of the best methods of cooling available though I rarely saw this procedure done well. Usually the use of concrete was done with minimum roof overhang, allowing direct solar gains into the living space as well as heating the building in general. I found no direct tie between Nan Madol as an archetype and the concrete houses that are being built today on Pohnpei. Similar architectural ruins can be found on Kosrae, again, however, no links were visible between the pre-historic architecture and the masonry buildings at present on the island.