Large slave labor forces, alien tech, or some form of magnetic force lifting that has been lost to the ages.
One man likely discovered (or rediscovered) a form of magnetic lifting in the early 20th century. His name was Ed Leedskalnin and he managed to
single handedly cut and manipulate into position large heavy pieces of coral into some strange monument. You can see his work at the site below.
www.coralcastle.com...


