It was quite an achievement for the Spanish to construct a fort made of tiny seashells. The Castillo de San Marcos stands on the shore of the intracoastal waterway in the historic city of St. Augustine, Florida and is a tourist attraction worth seeing. The builders had no idea if the enormous fort would stand strong against attacks when they used the coquina rock to build the thick walls. Coquina shells are tiny and numerous along the Florida coast, but you have to look as the surf recedes to see them digging into the sandy shoreline. The beach comes alive as the tiny Coquina quickly cover themselves again and again after the surf uncovers them. The sea birds love them as a meal and it looks to me like the shells are in a constant game of hide and seek – for their life!
The rock used to build the fort was brought in from an area just offshore and was cut to build the fort. When the first attack came, the Spanish were amazed at the way the cannonballs either bounced off or were embedded in the “rock” instead of crumbling it. Their hard work and choice of material had paid off.
Read more about the Castillo de San Marcos fort.