The stone city of Nan Madol, Phonpei. Using only primitive equipment the pre-contact Phonpeians quarried massive volcanic octagonal 'logs' weighing as much as 6 tons, to the shore, onto huge rafts, across the lagoon and precisely placed, with walls up to 20 feet high. The river image shows an exposed layer of the volcanic 'logs' similar to those used to create Nan Madol.