This National Monument is located in downtown St. Augustine, Florida. The fort is the oldest masonry fortification in the continental US. It was built by the Spanish using coquina shells for the walls. Coquina stone is formed from the shells of small clams. Over time, the shells compress together and have to be quarried similar to other stone. The coquina is more pliable when wet and becomes hard as it dries. The flexibility of the material allowed it to resist cannon balls from British attack. Once the fort was completed, homes near the fort were constructed with the same fire resistant material.
