This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Carve three nested squares joined by perpendicular lines into a flat stone surface and you have a Nine Men's Morris board, a shape simple enough that it turns up scratched into temple roofs in Egypt, cathedral cloister benches in England, and rock outcrops in Sri Lanka and Ireland, sometimes thousands of miles and centuries apart from any other example. That very simplicity is the problem for anyone trying to date or locate the game's origin: a grid this easy to scratch could have been carved by someone playing a game, or by someone marking out a completely different pattern for a completely different purpose, and stone does not record which.
The honest position, reflected in the open question attached to this entity, is that no single carved board can be trusted as proof of play without independent evidence, such as accompanying pieces or a written description, and no such independent evidence exists for the oldest candidate boards. What can be dated with confidence is the game's codified name and rules in medieval Europe, which is a real fact about Nine Men's Morris as an English pastime, but not the same thing as a real fact about where the game as a whole began.