Thanks, skr!
That was profoundly more information than I could deal with at one sitting, but it was fun to look!
Hmmm... All those mysterious circles...
Maybe they were trying to determine the equation for the circumference of a circle...
Speaking of mysteries post patterns, one of our favorite bass-fishing spots on the North River (couple miles north of where it empties into Albermarle Sound) is a small marshland bay of 4-to-6-foot water that has hundreds of submerged & rotted posts in a random pattern...
After much debate we finally decided that they had been put there by snake (cotton mouth) worshipers who, apparently, had mastered chaos theory...