In 1702, an English fleet sailing from colonial Carolina approached Castillo de San Marcos, a Spanish fortress on Florida’s sunny shores. Guarding the city of St. Augustine, the fort was an important political outpost that protected the Spanish empire’s trading routes. The English wanted to seize this garrison town from their archenemy, so their boats laid siege and spent two months bombarding the fortress with cannonball fire, to no avail. Despite the fierce attacks, the fort’s walls neither fell nor cracked. Instead, the cannonballs seemed to lodge in the walls, causing little damage — “as though you would stick a knife into cheese,” one Englishman observed. As they retreated, the English burned the city, but its residents stayed safe behind the fort’s mystical protection. The English tried again in 1740, but the infallible walls still stood strong against all odds.
Today, Castillo de San Marcos is the oldest masonry fort in the continental United States that has never been captured by force. And now we know the secret of its superpower: The fort’s walls were built from coquina, Spanish for “tiny shell,” a porous sedimentary rock formed from shells of dead marine creatures. When a cannonball hit, the shell pieces didn’t break but reshuffled around it as if absorbing the weapon, leaving the attackers bewildered.
Designated as a national monument and museum in 1924, Castillo de San Marcos has more than 300 years’ worth of history quite literally written on its thick, gray porous walls. It’s located within the remarkably old city of St. Augustine (founded in 1565), overlooking beautiful Matanzas Bay.
Plan Your Trip
Location: 1 S. Castillo Drive in St. Augustine, Florida
Getting there: The Castillo is within walking distance from St. Augustine’s city center and has a parking lot. Old Town Trolley Tours and Red Train Tours trolley offer hop-on/hop-off tours of St. Augustine that include stops at the fort.
Hours: Open daily 8:45 a.m. to 4:45 p.m.; closed Christmas Day
Admission: $15 for adults, good for seven consecutive days (Annual Senior Pass $20)
Tours: All tours are self-guided, but rangers are on hand to answer questions.
Best season to visit: From mid-September to mid-November, when crowds thin and summer heat subsides. Avoid rainy days because some of the fort’s attractions are located outside. It can get very hot, with a chance of thunderstorms on summer afternoons.
Accessibility: Fifteen of the 18 exhibits surrounding the Plaza de Armas are wheelchair-accessible, but bring your own chair if you think youll need one, because the museum has only one for emergency use. Accessing the Gun Deck requires climbing stairs.
Before you visit — or if you can’t visit — check out a virtual tour created by the National Park Service and the University of South Florida Libraries, where you can “walk” through the structure, learning as you go.
COVID-19 update: Castillo de San Marcos currently has a limit of 350 visitors, so there can be a line to enter. As per Centers for Disease Control and Prevention guidance, visitors are required to wear masks inside all park buildings, regardless of vaccination status. For updates, visit the park’s website.
What you’ll see
Spanish engineer Ignacio Daza designed Castillo de San Marcos as a hollow square with diamond-shaped bastions at each of its four corners. Named St. Pedro, St. Carlos, St. Augustine and St. Pablo, the bastions connect by thick walls that provided soldiers with a good overview of the area, particularly the sea, from which the Spanish expected most of the attacks to come. From the bastions they could also shoot at the enemy from multiple directions, creating a cross-fire effect. The walls, built from more than 400,000 blocks of coquina stone, with thickness ranging from 14 to 19 feet at the base and tapering to nine feet at the top, afforded the necessary protection from enemy fire.
When you purchase tickets at the Castillo’s entrance you also receive a self-guided tour brochure. As you walk in through the entrance known as the Sally Port, you’ll find the soldiers’ quarters to your right. These rooms, outfitted with wooden beds, tables and chairs stocked against the rough gray walls, help you imagine the lives of ordinary soldiers as they kept watch. “The Spanish garrison for St. Augustine was supposed to be 300 soldiers,” says Jill Leverett, a ranger at the fort, “but they were usually a little shy of that number because they were in the middle of nowhere.”
The soldiers didn’t live inside the fort — they usually stayed with their families in their St. Augustine homes — but instead they typically manned 24-hour shifts inside the Castillo. During these shifts, besides their guard duties, they took naps, played games, sought warmth next to fireplaces in winter and cooked food. You'll enter one room with a fully set dinner table, replete with a mock feast of vegetables, fruit, bread and wine. Nearby, an area that once served as the officers’ quarters is now a bookstore selling gifts and souvenirs, including pieces of coquina stone.