Oh, this is the grave marker of a "deserter" during the war of succession in the mid 1800's in the USA.  That is also known as the Civil War.  Deserters were generally brought to court and executed at the extreme, lesser punishment in other cases.  The flies made me think the plant had a "cactus aroma"  (like rotten substances) for pollination and that led to this..for what it is worth.    Strange one but a diti.