A smooth, white stone dating from the Roman era and unearthed in the Netherlands has long baffled researchers. Now, with the help of artificial intelligence , scientists believe they have cracked the mystery: the stone is an ancient board game and they have even guessed the rules. The circular piece of limestone has diagonal and straight lines cut into it. Using 3D imaging, scientists discovered some lines were deeper than others, suggesting pieces were moved along them, some more than others. "