The phrase, "written in stone" is used to emphasize that something is fixed and unchangeable; permanent.
Whether they are large or small, ornate or plain, headstones bear the names of friends and loved ones who have gone on before. Having their names "written in stone" marks their place of rest, and enables us to return to visit and pay them respect.
Did you know that the many pebbles and small stones resting on the tops of grave markers means that someone has paid a visit to a friend or loved one whose name is "written in stone?" This is a way of showing that a friend or loved one has not been forgotten.