Nan Madol is an archeological site located on the east coast of the island of Pohnpei, the main island of the state with the same name. This site is included on the UNESCO World Heritage Site list and has recently been on the list of endangered sites due to natural processes. The ruins of the city, built on artificial islands, surrounded by a stone wall and intersected canals, are often called "Venice of the Pacific" by visitors. The Nan Madol dates back to the 8th or 9th century. It reached its peak around 1628 when it was the center of the political and ceremonial life of a nation of about 25,000 people. According to legend, the twin wizards Olisihpa and Olosohpa built islands and a city with the help of a flying dragon, and the heirs of Olosohpa ruled for another 12 generations.