For more than 330 years, the Castillo de San Marcos has stood guard over the people of St. Augustine. During the first 100 years of the settlement’s existence, they built several wooden forts. The climate – and pirate torches – are rough on wooden structures so, after decades of requests, the Spanish crown agreed to pay for the construction of a stone fort.
There was just one problem. You don’t find a lot of stone in Florida. These Spanish settlers were quite resourceful and took advantage of an interesting shell rock found in the area. Called coquina (meaning little shells), it consists of many small shells fused together over time forming a sort of limerock. You’ll find coquina up and down the coast of Florida. The source of most of the Castillo’s construction material came from quarries on Anastasia Island – the barrier island protecting the settlement from the sea.
Coquina is easy to quarry. It is initially quite soft and can be cut with saws and axes. Once exposed to the air it hardens and changes color from orange to gray. It always remains quite porous. That turned out to be an advantage for the Castillo. Unlike normal rock, which shatters when hit by a cannonball, coquina either absorbed it like a sponge or it bounced off. As you walk around the fort today, you’ll see many holes where cannonballs and other shot penetrated some distance into the walls.
The Castillo was never captured in battle. Through the centuries it changed hands by treaty, but everyone who attacked the settlement after the fort was built went home in defeat. Coquina helped make that possible.
Coquina continues to be used in area construction. The house where I grew up had a coquina foundation and the original fireplaces were faced with the shell rock. It’s often used in landscaping – you’ll find several large pieces in my front yard. It’s one of many things that makes this area unique.
The Castillo de San Marcos is now a national monument and part of the National Park Service. You can visit the Castillo online to take a virtual tour of this amazing structure and learn more about its history.