America’s Spanish Fort – Castillo de San Marcos

(The following is based on reporting by Our Traveling Reporter, who’s been too busy to attend more shooting schools, as a student, anyway; but he has gotten some sightseeing in and deluged us with photos. We’ll be using the categories Fortifications and Historical Places to collect these stories in the weeks and months ahead. This is only the first of several photo-intensive posts on the Castillo de San Marcos — Ed.).

The Castillo de San Marcos — in English, Castle of Saint Mark — was a Spanish fortification meant to defend Spanish America against threats — spelled: Englishmen. This remarkable National Monument is little known by most Americans, but it’s one of the most interesting (as we’ll see in a future post, not the most interesting) military history sites on the northeastern coast of Florida, a peninsula that’s seen many flags and many fights over the years.

The Technology of the Fort

The Castillo is a fortification of stone on a typical 17th Century Vauban system (albeit, with some subsequent improvements). It looks to the casual viewer like a medieval castle, but it is a highly developed gunpowder-era fortification for fighting wars against sailing ships and land forces armed with the best cannon of the 17th and 18th centuries. The local stone, called coquina, is a sedimentary stone or limestone formed in large part of seashell fragments and sand. It is an almost ideal fort-building material: soft and easily formed when first quarried wet, but hardening to a concrete-like consistency after some months or years of air-drying. It proved to be very resistant to bombardment. Instead of shattering under cannon fire, the coquina blocks seemed to absorb the cannonballs. Twice, this led besiegers to give up and depart.

Spain constantly improved the technology of the fort, raising the walls and the bastions, and vaulting the interior rooms to allow heavy guns to be moved anywhere along the walls rather than just in reinforced areas.


Castillo de San Marcos, view generally North to South

The design of the fort is regular, symmetrical and repetitive for a reason. The advent of gunpowder caused a reassessment of fortifications that had been adequate in the day of weapons powered by muscle and sinew, and primitive, rock-throwing siege machines. The Elvis of fort design was a military engineer in the service of Louis XIV of France. The Sun King’s fort man, Sebastien le Prestre de Vauban, came to Louis as a captive, but changed sides, and went on to display his mastery of taking forts — and building them so as to make taking them difficult.

The Castillo strongly resembles a medieval castle, which makes sense when you think about it: even its name means “castle.” The Middle Ages are generally considered to end somewhere in the middle of the first millennium AD, and this fort began to be built shortly thereafter. Its basic shape is a rectangle, with a parade ground inside. Four diamond-shaped strongpoints called bastions provide mutually supporting fire and ensure that every wall exposed to an attacking enemy can be swept by fire.

The corner bastions allowed cannons, musketeers and archers to cover the long walls and take any assaults under enfilading fire. When the fort was originally constructed, the bastions, three of which are solidly filled inside (the fourth is solidly filled, apart from a vaulted powder magazine), were the only part of the structure that could support the weight of cannon.

A fifth “bastion,” an irregular heptagon, is the ravelin, a structure that provides the only way in and out of the fort, and that protects the gate in the fort wall from observation and direct fire. The NPS calls it a demilune, the difference between the two being somewhat hazy in military engineering.

The seawall is part of the overall fortification model, and is made of an inner and outer wall of the same coquina that built the fort, stuffed with rocks and earth. The coquina blocks are set in ashlar and the wall was topped with granite, providing a promenade in peacetime and a firing position in war. The initial wall lasted a century; it was rebuilt by West Point-trained engineers during the US Territorial period after Spain ceded Florida in 1821. (They used the same materials as their Spanish predecessors. Don’t mess with success). That wall lasted, with some deterioration, until powerful hurricanes in the 21st Century damaged it; a rebuild project is underway to protect the historic wall with a modern concrete wall to seaward.

The landward sides of the Castillo were protected by a glacis of earth, designed to stop cannonballs or deflect them over the fort entirely. The fort side of the glacis terminates in a retaining wall, creating a covered and concealed pathway allowing defenders to move without being exposed to observation and direct fire. This is called the covered or covert path. In times of war, additional works of earth and would be constructed out beyond the glacis, providing further defense in depth.


Moat, shown on NPS brochure. Definitely worth a click to embiggen.

There is also a moat, which nowadays seems to be kept dry deliberately, but which was flooded originally and at least as late as our first visit in 1974. The moat flooded tidally to a shallow depth, but could be flooded deeper through a system of locks and gates. It is one more sign that this fort didn’t just happen, but was engineered in every detail.

A fort implies the potential for siege warfare. Sieges that end in attacker victory usually end, not when the walls come tumbling down, but when the defenders lose heart or run out of food and (especially) water (or the attackers contaminate the water supply). The Spanish builders of the Castillo considered this. They had large storerooms and not one, but three, protected springs inside the castle. (One remains in service today, 350-plus years later). The water table is close enough to the surface — it is Florida, after all — that even if all springs were somehow destroyed, a new one could be quickly established.

The Spanish considered their faith a bastion against defeat by loss of morale (there was always a religious subtext to Spanish Catholic wars with Protestant England). They incorporated a chapel in the Fort’s design and named its prominent features after Catholic saints, to whom they prayed for Divine intercession.

Sieges that end in defender victory, conversely, usually end when the attackers lose heart, run low on supplies, or are attrited (more usually by disease and malnutrition than by enemy action), although sometimes a relief force lifts the siege by defeating the attackers or leveraging them out of position.

History of the Fort

The Spaniards began constructing it in the 1660s, after a previous wooden fort was burnt and the town sacked by pirates, and the first stone was laid in 1672. We know the name of the engineer who was sent from Spain to design and supervise the construction of the fort, Ignacio Daza, although we know little else about him. The fort was completed — to the extent that any fortification is completed — in 1695. It would have been faster, but Daza was at the end of a long pipeline, and even at home, Spain was always short of money and skilled artisans. The Florida coast was not a perfect environment for European life, either. If the pirate sacking of 1688 wasn’t enough, the Spanish were motivated by the new English colony just up the coast at Charleston; they knew that the kings of Europe seldom went long between wars, and when Spain and England warred again, the more-numerous English would come for Spanish America.

When construction began, San Augustin had been a Spanish city for over 100 years. But the growing British strength in the New World threatened San Augustin. The fort was tested soon after its completion by a British siege in 1702. The civil population crammed into the fort, the city burned, but the fort held until a Spanish squadron relieved the city. Trapped between the stronger Spanish fleet and the shore, the British burned their ships and departed overland to Charleston. After a period of some decades of peace, Britain and Spain were at war again in the War of Jenkins’s Ear (yes, that’s really its name. Google is your friend).

In 1740, the British tried again with a better thought out attack plan, but they still wound up defeated by the coquina stone walls.

The Castillo stood against the English for a long time. In the end, it fell not to the sword but to the terms of a treaty dictated after a Spanish defeat on other fields. By the time the Revolution came to the Colonies, it was a British garrison, won by Britain by defeating Spain (a French ally) in the Seven Years’ War in 1763. During the long American War of Independence, Colonial forces never put pressure on the fort, and it was a backwater of the War of Independence. By the Treaty of Paris which recognized American independence, it reverted to Spanish sovereignty. The colony was more of a burden than a boon to a troubled Spanish monarchy, and the United States purchased it from Spain in 1821. It flew the Stars and Stripes for the next 40 years, becoming a Confederate fortification without a fight in 1861, and reverting to the Union just as peacefully in the spring of 1865 on the defeat of the Confederacy. Throughout the 19th Century, it was widely used as a prison for Indians, both from the Seminole Wars and plains Indians, removed to Florida, far from their supporters. During the Seminole War, these Native Floridians cemented their reputation as hard cases — it was the most costly Indian war from the whites’ standpoint — but most of the native American prisoners here were Plains Indians. It seems that important chiefs were sent to San Marcos. It was the Gitmo of its day, or perhaps Alcatraz for Indians.

When the Castillo de San Marcos became part of the US coastal fortification system, like all the forts in the system, it had periods of improvement and periods of stagnation, if not neglect. The American owners filled in the part of the moat between the fort’s eastern wall and the seawall, and used it to site a battery of then-new Parrott guns, extending the fort’s reach to sea. To increase the guns’ threat to the wooden sailing warships of the day, a stone furnace was built behind this battery to heat shot red-hot, adding the threat of shipboard fires to the woes of any attacking naval squadron.


Castillo Park Service SignBy 1933 it was a white elephant burdening the US Army. Coquina is awesome stuff, but it wasn’t made to withstand breechloading artillery; new concepts in coastal defense used smaller, concealable, reinforced-concrete gun emplacements linked by electric communications to remote observation and fire-control facilities, integrated with command-armed and -detonated minefields air patrols. Furthermore, the Indians were off the warpath for good, and Americans had no stomach for locking them up. With no practical use in hand for the old fort, and a Depression squeezing everybody, they pushed it off onto the Department of the Interior. Now it is a national monument, maintained with pride by the National Park Service.

Castillo EngineersIt has also been recognized as a civil engineering monument by the American Society of Civil Engineers. One doesn’t think much about the technology that went into building a mighty fortress in the centuries before steam, but the Engineers apparently did.

You might wonder, in all those different phases of ownership, how many times the Fort has been abandoned, derelict, in ruins, or restored. The answer is — none. The Castillo withstood the attacks of 1702 and 1740 with aplomb, and perhaps more impressively, has shrugged off centuries of assault by the elements. All of the fort’s many changes of flag have been done peacefully, as a result of wars decided or treaties contracted in other places. The Park Service has done some excavation and restoration to the grounds, and keeps up with the maintenance, as the Army did.

Conversely, an out-fortress at Matanzas, built after the 1740 attack, was allowed to go to ruin, but has since been restored.

After the For More Information section below, there’s a “more” button — and with it, you’ll find some photos taken at Castillo de San Marcos recently by Our Traveling Reporter. We’ll have more photos, and more information links, in future reports.


This post has been corrected. We had used both terms ravelin and demilune without making it crystal clear we’re applying them both to the same structure, the low bastion-like element that guards the approach to the sally port. NPS prefers demilune.

For More Information

Fortified Places:

The terminology of a Fortress:

A Photo Tour of San Marcos — Part I of ?

All these pictures were shot by Our Traveling Reporter, except as noted. They all will embiggen with a click.

The Park Service has done a really nice job with the signage -- between the signs and brochures, a self-guided tour is a real possibility.

The Park Service has done a really nice job with the signage — between the signs and brochures, a self-guided tour is a real possibility.

Motor vehicles are kept at a safe distance and tourists approach on foot (or on wheels, if that's how you, uh, roll, but the wheelchair access isn't unlimited). The seawall -- and the inlet -- are on the right, and you can see the Castillo's imposing silhouette dead ahead.

Motor vehicles are kept at a safe distance and tourists approach on foot (or on wheels, if that’s how you, uh, roll, but the wheelchair access isn’t unlimited).

Looking at the photo above, the seawall — and the inlet — are on the right, and you can see the Castillo’s imposing silhouette dead ahead. Note that the pathway cuts through the covert way or covered path, and there is a rising glacis before the covered way.

You can see why San Marcos is a staple of picture postcards -- and why it withstood two attacks from the sea in the background.

You can see why San Marcos is a staple of picture postcards — and why it withstood two attacks from the sea in the background.

The area in the foreground is actually a moat, which was flooded daily by the tides (and the defenders could close gates at high tide to retain the water). Even in the 20th Century, the moat was sometimes water-filled.

Around this corner is the section of the moat that was filled in during the mid-19th Century to allow the US Army to emplace a battery of Parrott guns, early banded/reinforced muzzleloaders.

Sally-port into the Demilune, showing a Spanish crest.

Sally-port into the Demilune, showing a Spanish crest.

These Spanish escutcheons have been restored relatively recently. We wonder what the heraldic elements of the crest mean. It looks like a scrawny pig is holding the whole thing up! Via an Iron Cross, no less. That’s probably not what the thing really symbolizes.

A lot of effort goes into keeping the old fort a showplace.

The Demilune is the structure that looks like (but isn’t) a fifth, stand-alone bastion. It shields the one sally port in the fort’s walls from observation and direct fire, and during a siege would be manned by a contingent prepared to keep fighting even if cut off by enemy forces swarming the moat. Passing through the sally port, one can’t help but be struck by how difficult the port would be to force, given the military technology of the 1600s through the 1800s.

It would also be a really good place for your tribe to hole up in the Zombie Apocalypse. Unless the undead climb stone walls well.

Drawbridge. Yes, that is really a thing.

Drawbridge. Yes, that is really a thing. This is the drawbridge to keep you out of the Demilune (left and middle of photo), but there’s another one at the sally port in the main fortress wall (visible right).

Vauban and his followers knew that any obstacle, even covered by observation and direct fire, would only delay and perhaps bleed a determined enemy. Therefore, in forts of this vintage it’s not at all unusual to see defenses in depth, so that each obstacle overcome leaves the enemy facing another obstacle.

After passing the Demilune and its drawbridge, you have to cross an elevated causeway across the (now grassy) moat to the sally port's drawbridge.

After passing the Demilune and its drawbridge, you have to cross an elevated causeway across the (now grassy) moat to the sally port’s drawbridge.

In the photo above, you can see just how thoroughly the approach was covered. Look at those cannons and imagine the wall also lined with musketeers or even archers. But that’s not the half of it. You can’t see it here, but the bastions outside that photo to the left and right enfilade this section of moat on both sides. (That’s why forts have bastions, after all).

Tis post, taken from near the first drawbridge shot, shows you the moat and the way the bastion in the background enfilades the only approach to the only opening in these strong cochina walls.

Tis post, taken from near the first drawbridge shot, shows you the moat and the way the bastion in the background enfilades the only approach to the only opening in these strong coquina walls. The crenellations with cannon, on the right, are on the “front” wall of the Castillo; the two crenellations dead ahead are on a bastion wall, one at 90º to the “front” wall.

Cannon and the Florida flag. This fort's seen a lot of flags!

One of the Bastions, Cannon and the Florida flag. This fort’s seen a lot of flags!

Drawbridge again

Drawbridge again. Looking back to the tourists’ approach route.


View from the top of the Demilune.

Main Gate. Note that it has a Portcullis.

Main Gate. Note that it has a Portcullis.

Changing of the Guard. A band of reenactors/interpreters plays...

Changing of the Guard. A band of reenactors/interpreters plays…

... while the guard mount marches into position.

… while the guard mount marches into position.

We have to wonder, how did the British Redcoats and the Spanish troops in, well, red coats, ever keep each other straight? We guess if the Spaniards were holed up in the Castillo, they could just assume anything outside these walls was enemy.

Spain was often France’s ally during centuries of war with Britain. They fought over colonies, the Netherlands, various disputed dukedoms, trade, and sometimes, general principles. There was also a religious angle — Henry VIII dispossessed the Catholic Church of most of its wealth and established a new Church of England with himself at its head; the Spanish monarchy was orthodox (small-“o”) Catholic.


There is a book and gift shop. The books for sale include:

Bannon, John Francis. The Spanish Borderlands Frontier: 1513-1821.
Francis, J. Michael: St. Augustine, America’s First City: A Story of Unbroken History and Enduring Spirit. 
Quesada, Alejandro: Spanish Colonial Fortifications in North America 1565-1822 (Shown)
Unknown. The History of Castillo de San Marcos, St. Augustine, Florida.


Coquina sample. So that’s what this mighty stuff looks like up close!

And that’s probably a good place to stop for now. More of the Castillo tomorrow, perhaps, and in the coming week.

16 thoughts on “America’s Spanish Fort – Castillo de San Marcos

  1. S

    Thanks for this post, and to the TR for the pics.

    You asked about the coat of arms… I had to know too and dug something up.

    It is the Coronela, the King’s colour, a simplified form of the Spanish arms; symbol of the foot troops. The castle and lion stand for Castile and Leon. The little piggy is the Order of the Golden Fleece, Spanish version. The iron cross could be for the Order of Ferdinand. The flag the fort is flying is the Cross of Burgundy, a version of the Cross of St Andrew.


    Fascinating stuff…thank you.

    A small typo…”…detonated minefields air patrols” should probably be something different.


    Fascinating stuff…thank you. I love looking at Vauban fortifications…he was truly a genius. Absolutely everything is covered by enfilade fire and view, and yet so beautiful as well, as all great enginnering should be.

    A small typo…”…detonated minefields air patrols” should probably be something different.

  4. RobRoySimmons

    Thanks, perhaps the only reason I would play tourist in FLA would be to see the Spanish forts

  5. Ken

    St. Augustine is a fine place to spend a few days. Lots of interesting things to see and good food to eat.

  6. Sommerbiwak

    Interesting. I really have to read more about fortifications in 17/18/19th century.

    The average USian has the bad habit of ignoring pre english colonisation history I think. Although there actually is quite a lot of this all over the USA.

  7. Winston Smith

    Visited this fort as a small kid and never remembered where it was other than some nebulous place on the east coast of Floriduh. Always wanted to go back and now that I know where it is, I can. THANK YOU for this post.

  8. Slow Joe Crow

    This is a great presentation about a fort I only vaguely knew about. One question for you or TR, are the small cylindrical sentry posts on the points of the bastions unique to Spanish fortifications? I don’t recall seeing them on English built Vauban forts like Ticonderoga, or the later parts of Dover Castle.

    1. Hognose Post author

      Joe, the technical term is bartizan, which certainly suggests Spanish origin. A quick google tells me that survivors are primarily found in Spanish fort architecture, but English and Scottish strongpoints used them also. While scholars seem to use the term “bartizan,” laymen in English often call them “corner turrets.” Only the Spanish examples seem to have roofs. They can be cylinders like San Marcos’s, squares (easier to build) or hexagon shapes. You are right on, in calling them “sentry posts,” about their raison d’être; they’re there so a sentry or watchman can step out and get an eye on the face walls of the bastion. Accordingly, you only see these on corners of angular fortifications, where straight walls join at an angle, not circular fortifications, except for fictional, fantasy or symbolic fortifications. A bartizan doesn’t work if the wall curves away from the sentry’s line of sight!

      Bartizans tend to be cantilevered out from the walls. A bastion is much larger than a bartizan and is built from the foundation up.

  9. "Greg"

    I would LOVE for someone to tell me the story behind the origin of the term “sally port”… EVERY jail that I have been to (and I’m talking west coast to east coast, Maine to Florida & Seattle to San Diego has used that term to refer to the secure entrance where vehicles carrying prisoners enter and exit. No one has ever been able to answer that question…err update: google/wikipedia has given considerable detail, it’s been a while since the last time i checked to see what answer i could find to that question… and now, I think i will google “war of jenkin’s ear”!!

    1. Hognose Post author

      If you’ve been to that many jails, you need to try harder to stay out of trouble.

      The origin of the term is this: from the “sally port” defenders would sally out, to test the besiegers. The term is quite ancient and appears in Middle Ages documents, if not earlier. I expect it was a rather short step from the use of this term in fortification architecture, to the use of this term in corrections architecture.

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  11. staghounds

    It’s amazing how similar the Vauban star forts are- quite a brand success. Here’s Bourtange, which is quite a miniature San Marcos in the middle of the Dutch plains-

  12. Docduracoat

    Puerto Rico is in the United States.
    The El Morro Fort in San Juan was built over a time period of 150 years.
    It has been the scene of bloody battles, and changed hands by force many times.
    It is maintained in perfect condition and is extremely interesting to visit.
    Havana Cuba also has a spectacular Spanish fort.
    They have fired one cannon shot every night at 9 pm for 200 years straight except during world war 2.
    Providencia’s sister island, Santa Catalina island, has a pirate fort.
    It is interesting as a contrast to a proper military fort. Looks like a couple of Yahoos piled up some rocks and mounted a few cannon on top.
    Sail from Florida around the carribbean and you will be amazed at how bloody the history of the area was.

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