Written around 1500 by a Franciscan friar and mathematician, Luca Pacioli, De Ludo Schacorum is a collection of chess puzzles that are no different to what we find today in newspapers or magazines.
In most contemporary depictions, the pieces were represented by letters or numbers. Two depictions used figures, but they were crude, like the chess pieces of the day.
In De Ludo Schacorum, also known as the Schifanoia (the "Boredom Dodger"), king, queen, bishop and knight are all represented by elegant and distinctive symbols.
A Milanese sculptor and architect, told the Guardian that was just one of several reasons why he was "more than certain" that the illustrations were Leonardo's.
The clue to a da Vinci connection is the so-called Golden Mean.
Read more in The Guardian: The Last Supper - now how about a nice game of chess?