During Post-classical Times the Micronesian and the Polynesian peoples constructed cities in some areas such as Nan Madol and Mu'a. Around 1200 AD the Tu'i Tonga Empire spread its influence far and wide throughout the South Pacific Islands, being described by academics as a maritime chiefdom which used trade networks to keep power centralized around the king's capital. Polynesians on outrigger canoes discovered and colonized some of the last uninhabited islands of earth. Hawaii, New Zealand and Easter Island were among the final places to be reached, settlers discovering pristine lands. Oral Tradition claimed that navigator Ui-te-Rangiora discovered icebergs in the Southern Ocean. In exploring and settling, Polynesian settlers did not strike at random but used their knowledge of wind and water currents to reach their destinations.