Fort Massachusetts' second 15-inch Rodman didn't survive the 19th century. The bain of historic American artillery were the scrap drives of the Second World War: Communities competed with each other to donate the most scrap iron for the war effort, and frequently went overboard in regards to leftover Civil War cannon. I've heard that these scrap drives ultimately contributed a negligible amount of useful product to the military, but served as a way for folks on the home front to feel they were doing their part. I can only assume that this fetching pile of iron still sits where it does today because of its distance from convenient modes of transport.
The sign to the right is Pieces of the Past.