Built as a complex of artificial islands, Nan Madol was constructed with openings in its seawalls and breakwaters for the purpose of channeling seawater to altars during important religious ceremonies channeling seawater to altars during important religious ceremonies A routing water under the floor of royal residences to provide a cooling effect routing water under the floor of royal residences to provide a cooling effect B irrigating agricultural areas used to grow food supplies inside the complex irrigating agricultural areas used to grow food supplies inside the complex C providing a flow of water through the canals during the changing tides