The walls excist out of loose bricks in a basket-work. The holes between the blocks are filled up with grit. The basaltblocks have a length of 10 till 27 feet. Their weight is between 900 and 2200 kilo each. It seems that the bricks are all cut out and size-made for their destination.
Nobody knows the exact origin of the ruins.
There are legends about the origin of Nan Madol. The blocks came from the north coast of Ponape, that is the place where basalt is produced, and were taken to almost the other side of Ponape. The cutting out of the 10 till 27 feet long, hundreds of kilo's weighting blocks seems to be a extreme laborious job. But the transport of the blocks seems to be a impossible task, even with an army of strong people. At the route from the place where basalt is produced to Nan Madol, lie several basaltblocks in the ocean.