The stone is decorated with prehistoric rock art, and whoever constructed the souterrain simply incorporated it into the fabric of the structure, reusing something far older as though it were ordinary building material.

A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval ringforts in Ireland, and most likely used for storage or refuge. The one at Emper follows a fairly recognisable plan: an entrance on the north side of the ringfort interior opens into a well-constructed stone-built chamber, from which two passages extend in different directions. It is in the right-hand passage that the decorated stone appears, set into the wall on the right-hand side. As O'Reilly noted in a 2010 article on rock art in County Westmeath, the stone is long and carries prehistoric incised markings, making it considerably older than the souterrain itself. The exact age of the rock art is unknown, but such carvings in Ireland are generally associated with the Bronze Age or earlier. The people who built the souterrain were almost certainly not its makers.