“sweet potato”
Amazing coincidence that I just watched an old Arthur C. Clarke episode of his series debunking weird science stories recently. They set up a bunch of guys to roll Easter Island statue size weights on wooden log rollers and pull them.
They had found evidence that sweet potatoes were originally used underneath to provide a slippery surface. But there weren’t any grown locally and the TV series guys had to buy hundreds of pounds of regular potatoes. The system worked.
Since then they’ve found a system of moving the things more easily...by rocking them. It explains the peculiar shape of the base as well.