This Ancient Roman Game Board Was a Mystery. Researchers Used A.I. to Figure Out How to Play

The limestone oval is carved with a dark, thin rectangle on which ancient people repeatedly moved game pieces

More than a century ago, a scratched-up slab of limestone was excavated in the modern-day Netherlands and later deemed an ancient Roman game board. Since then, the mysterious game has eluded historians. But according to a study recently published in the journal Antiquity, researchers might have figured out how to play it.

Walter Crist, who researches ancient games at Leiden University in the Netherlands, first saw the carved limestone in 2020, at the Het Romeins Museum. Located in the southern Dutch city of Heerlen, the museum focuses on the local history of the Roman Empire, which expanded into Northern Europe in the first century. 

“They had this thing that they were calling a game,” Crist tells NPR’s Henry Larson. “I looked at it and it was interesting to me because it was not a pattern that I had really recognized.” Crist adds, “It’s this oval-shaped stone, quite thick, so you can see the chiseling in this shape to have this surface on the top.” 

Crist wasn’t sure about the artifact’s board game label, he tells NPR, but then he noticed that from a specific angle, he could see distinct marks of wear. They signaled that long ago, people repeatedly slid hard pieces over the rock in the same patterns—a clear indication of play. Crist and a team of researchers aimed to learn the rules of the limestone slab’s game.

According to a statement from Antiquity, nearly all the world’s cultures have played board games since at least the Bronze Age—which began around 3000 B.C.E.—but many such games haven’t survived, lacking archaeological evidence. The Coriovallum limestone game board, while physically preserved, lacks written records. The researchers knew the artifact was excavated in Heerlen in the late 19th or early 20th century, and that it was carved from French limestone, reports Scientific American’s Jackie Flynn Mogensen. But the researchers didn’t have much more than those facts—let alone a written rulebook.

“It's the kind of thing that we still experience today with things like checkers or tic-tac-toe,” Crist tells NPR. “You probably learned it from somebody who knew how to play it.

So the researchers began looking at other old European games, hoping to find something similar to the carved limestone. They searched the Ludii games database, “the largest comprehensive database of traditional board game rules currently available,” per the study. The team was looking for “games that were on smallish game boards,” on which pieces can take a maximum of 22 different positions, Crist tells NPR.

“You can find sort of families of games that have some similarities,” Barbara Carè, an archaeologist at the University of Lausanne who wasn’t involved in the study, tells NPR. “So you may attempt to reconstruct the evolution of a game from maybe a basic, ancient form to a more developed one.”

The researchers also obtained a clearer view of the stone’s physical wear patterns. Luk van Goor of Restaura, a local business that conserves and restores archaeological objects, made “extremely detailed 3D scans” of the game board, per a statement from Maastricht University.

“Those scans reveal a lot of details of the lines, and they show that some of these lines are a fraction of a millimeter deeper than others,” Crist says in Maastricht’s statement. “Those deeper lines were used more intensively.”

The researchers then brought A.I. into the fold. Ludii isn’t only a games database; it’s a general game-playing system, a form of A.I. that can deduce game rules, says Dennis Soemers, a computer scientist at Maastricht University, in Maastricht’s statement.

“We trained Ludii with the rules of about a hundred medieval or older games from the same cultural area as the Roman stone,” Soemers says. “Ludii 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.”

The researchers programmed two A.I. bots to play on a digital version of the limestone board, using more than 100 different sets of rules from other known games. The bots played 1,000 rounds of each game, and Crist’s team tracked gamepiece movements throughout. They then matched the limestone board’s wear marks to the movement patterns of the Ludii games.

Nine rule sets in the database appeared “consistent” with the limestone board’s wear patterns, Crist tells Scientific American. “And they were all variations of this same kind of blocking game.”

This “blocking game” would have involved two players moving small pieces—likely made of glass, bone or earthenware—along the lines of the board, with one attempting to trap the other’s pieces in a corner.

The researchers dubbed the limestone board Ludus Coriovalli, Latin for the “Coriovallum Game.” It’s now available for play on Ludii: Users can choose one of the nine blocking game rule sets found by the researchers, then play against a bot.

Soemers hesitates to claim that the researchers matched the limestone board to its exact intended rules. “If you present Ludii with a line pattern like the one on the stone, it will always find game rules,” he says in Maastricht’s statement. “Therefore, we cannot be sure that the Romans played it in precisely that way.”

The study is “groundbreaking,” Véronique Dasen, an archaeologist at the University of Fribourg, tells Science News’ Tom Metcalfe. Dasen adds that similar A.I.-powered research techniques could be used to investigate other “lost” games.

Games have long been integral to anthropological research. They help researchers understand more about how societies socialize and pursue pleasure. Ancient Romans, historians know, enjoyed many games—apart from the bloody gladiatorial battles they watched in the Colosseum. They had a circular game called Rota, which was a lot like tic-tac-toe, and another called Ludus Calculorum, similar to Gomoku.

But until now, there hasn’t been evidence that Romans had access to blocking games, which were previously thought to have originated in early medieval Europe. The new study may push back their origins a full millennium, through one unpopular game, demonstrating board games’ ephemeral nature in history.

“Games can go on for centuries,” Dasen tells Science News, “and sometimes they appear and then disappear.”