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.

"We can see wear along the lines on the stone, exactly where you would slide a piece," said Walter Crist, an archaeologist at Leiden University who specializes in ancient games.

Other researchers at Maastricht University then used an artificial intelligence program that can deduce the rules to ancient games.

They trained this AI, baptized Ludii, with the rules of about 100 ancient games from the same area as the Roman stone.

The computer "produced dozens of possible rule sets. It then played the game against itself and identified a few variants that are enjoyable for humans to play," said Dennis Soemers, from Maastricht University.

They then cross-checked the possible rules with the wear on the stone to uncover the most likely set of movements in the game.

However, Soemers also sounded a note of caution.

"If you present Ludii with a line pattern like the one on the stone, it will always find game rules. Therefore, we cannot be sure that the Romans played it in precisely that way," he said.

The aim of the "deceptively simple but thrilling strategy game" was to hunt and trap the opponent's pieces in as few moves as possible.

The research and the possible rules were published in the journal Antiquity.