Much has been made of the technology required to produce such solid rock spheres, leading to suggestions of advanced techniques, machinery, or even alien intervention.
I downloaded a number of pictures of these stone balls, which are shown in the montage at left. Overlaid on each is a translucent perfect circle. It's obvious these stones are amazingly spherical. Some theories for their construction include the melting of stone and subsequent pouring into giant molds. Of course, the mold would have to be carved, right? Regardless, either carved or molded, their existence from thousands of years ago does not seem possible. As if the universe wasn't mysterious enough already.