In Saint Augustine, Florida there is a lovely Spanish Fort called Castillo de San Marcos which is now a National Monument. It dates back to 1672 and is the oldest and largest masonry fort built in the continental United States. The walls are made of enduring “Coccina Stone” cut from a nearby quarry. This was made up of tiny coccina shells and sand that hardened into the white stone. Here is one corner of the fort with palm trees near the shoreline.