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.
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.
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.
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.
In the Plaza de Armas, the fort’s courtyard, you’ll see one of the three original wells, still with freshwater. The well is a good spot to start exploring various exhibits in the rooms surrounding the plaza. As you follow the self-guided tour clockwise around the courtyard, posters walk you chronologically through the fort’s construction and history. Fires, rot, storms, termites and tides destroyed St. Augustine’s first nine wooden forts, so the Spanish began building this stone one in 1672, a project not completed until 1695. Historians believe they used, at least in part, African laborers (both free and enslaved) and Native American tribesmen (who were paid but forced to work). The laborers quarried more than 150 million pounds of coquina, then barged the blocks across the bay to the site, and laid them into walls, all by hand. In the 18th century, the Spanish further fortified the Castillo. It’s not clear whether they knew about coquina’s special properties. “It’s possible that they didn’t, which is why they made the walls so thick,” says Leverett.
As you continue the self-tour, you’ll see storage rooms where the Spanish stockpiled ammunition, gunpowder and tools, as well as provisions such as beans, corn, flour and rice. A gunpowder room looks more like a crawlspace with a door about 3 feet high, which children frequently crawl through to explore the room. Several rooms convey the fort’s history under the English governance, after the Britixh took Florida from the Spanish in 1763.
You can also learn about the fort's 19th-century history: After Florida became part of the U.S. in 1821, the fort was renamed Fort Marion in honor of Revolutionary War officer Francis Marion, known as the Swamp Fox. Its Fort Marion days included some grim happenings, such as its use from 1875 to 1878 to imprison 74 Native-Americans from five tribes, many of them survivors of the brutal Sand Creek Massacre of 1864 in what’s now Colorado. (Congress officially changed the national monument’s name back to Castillo de San Marcos in 1942.)
Once you complete the fort walk-around, take a moment to stand in the middle of Plaza de Armas to imagine being here in the turbulent colonial era. In peacetime, soldiers practiced their military skills on the plaza to commit musket use to muscle memory, crucial for battle. When an enemy threatened, the residents of the surrounding St. Augustine flocked here for safety, building shelters on the plaza and cooking food. In the 1702 siege, about 1,500 soldiers and civilians lived inside the fort for 51 days — a feat unimaginable by modern standards.
If you’re able, climb the staircase to the bastions and the Gun Deck. There’s no elevator or wheelchair access, but the stairs aren’t steep with all 47 steps big and wide. On the deck are cannons that were used to return fire — some original, others replicas. You’ll also be rewarded with a refreshing wind, spectacular view of Matanzas Bay and the possible sighting of a dolphin or two. Looking out to sea, visualize approaching enemy ships dropping anchor and pummeling the fort, and sense the attackers’ frustration and bewilderment at its impenetrable walls. You won’t find any cannonballs lodged in the walls because the Spanish replaced damaged sections with new pieces, but you can imagine this peculiar sight.
Before the pandemic, fort staffers dressed in Spanish costumes and fired the cannons on weekends, paying tribute to the fort’s tumultuous history, but the program is currently suspended to avoid attracting large crowds. Similarly, rangers’ talks, formerly given several times a day at Plaza de Armas, are suspended, but rangers are on hand to answer questions.
Ranger’s tip: The popular museum has a small parking lot that tends to fill up on busy days. To get a spot, particularly near the entrance, Leverett suggests coming early. Alternatively, you can park your car at one of the city’s parking lots or garages and walk 10 to 15 minutes, or take a trolley.
Join today and save 43% off the standard annual rate. Get instant access to discounts, programs, services, and the information you need to benefit every area of your life.
Pirate and Treasure Museum: Only a three-minute walk west, this museum unveils truths and myths about the area’s famous buccaneers. Also learn why Spanish explorer Ponce de León named the land Florida while he was searching for the fountain of youth, believed to exist in the New World.
Anastasia State Park: About a 10-minute drive south of the fort, this park is where the Spanish mined the coquina stone. It’s now a wildlife refuge with 1,600 acres of pristine beaches open to the public ($4–$8 for parking).
Where to stay
Splurge: St. Francis Inn is a bed-and-breakfast property about a 10-minute drive south of Castillo de San Marcos, with 19 plush, uniquely decorated rooms. Come evening, roast marshmallows on the firepit in its charming courtyard. Rooms from $179
Save: Located near St. Augustine’s historic center, the Best Western Bayfront is just a four-minute walk south of the fort and other downtown attractions. It offers 59 comfortable rooms and efficiency suites. Rooms from $139
Where to eat
Splurge: Dine on European-style favorites such as Beef Wellington and lamb chops at the Raintree Restaurant in St. Augustine. Don’t miss the Eggs Benedict Arnold at its popular Sunday brunch. The eggs pair nicely with the Breakfast Bloody Mary, which includes vodka, bacon and shrimp (seriously).
Save: Enjoy a seaside view of the Castillo at Meehan’s Irish Pub & Seafood House. You might order a Guinness stout, fish and chips and, for dessert, Jameson bread pudding.