The Famous Fort in St. Augustine That Was Built of Seashells

Castillo de San Marcos historic fort
the Castillo de San Marcos fort
Castillo de San Marcos Fort in St. Augustine, Florida

Photo credit: By National Park Service ( [Public domain], via Wikimedia Commons – click the photo to visit the page.
One area of Florida that is worth the visit is historic St. Augustine. Henry Flagler took an interest in the area and built the Ponce de Leon Hotel which is now Flagler College. Visitors began coming and haven’t stopped. But that is another story.

I recently took another trip to St. Augustine and you can read about it here.

I find the history of the old fort in St. Augustine, Florida fascinating. Located on the east coast of Florida, the Castillo de San Marcos (which means St. Mark’s Castle) is right on the Intracoastal Waterway.  Today it serves as a tourist attraction with many visitors trudging over those thick walls each day, but it was built long ago to protect the people of a Spanish settlement.

The Spanish settled in the St. Augustine in 1565 and built forts of wood which were too easily destroyed.  Flimsy wood was either burned by attackers, or destroyed by storms. They needed a better and sturdier line of defense.  So they came up with an ingenious idea.

The state of Florida doesn’t have many rocks.  The entire state is very sandy, but of course there is lots of water, and the fort sits right on the ocean.  The builders were resourceful and decided to use hardened shell rock, called ‘coquina‘ which was abundant just off the coast on an island (now, Anastasia Island).   The coquina shell is a tiny thing, but when it’s crushed and compressed with many like it by the sea, it becomes rock-like.  No one was sure how well this coquina material would work, but I suppose their options were limited!

coquina shell
Coquina shell

Construction on the fort began in 1672.   The coquina material was cut into sections.   Oyster shells were burned to make lime, which was added to sand, which made a mixture that resembled cement.   And that is how they went about building this massive structure.  It took 23 years to complete.

When the walls were being constructed, no one knew for sure how well the coquina rock would hold up against cannon fire.  Only 7 years after the completion of the fort, they had a chance to find out.   When the British attacked, those thick walls – some of the fort’s walls are up to 19 feet wide – held up even better than expected, and the attack failed.

coquina rock wall
Tiny shells can be seen in this close up photo of the fort’s wall. (my photo)

It turned out that the seashell walls would give a little when hit, and the cannon balls would either bounce off, or become imbedded.

In 1924 the Castillo de San Marcos fort was declared a national monument.  Please read more about it here.

St. Augustine has much more to see than just the famous fort.  It’s one of my favorite areas of the state.   When you visit, plan to spend the entire day there, traveling through the city on trolley tours, taking a horse drawn buggy ride, shopping, eating, and visiting museums.   The Ripley’s Believe it or Not museum is worth a visit.

Author: Pam

Spending time on the water is the best, and blogging about the sea life found along the saltwater river and ocean is what I do. I’m also a designer at Zazzle and sell my work, with a lot of ocean themes, on the site.

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