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Castillo de San Marcos fort in St. Augustine, Florida, USA. Photo By I, Jonathan Zander –

Top 10 Interesting Facts About Castillo De San Marcos

The Castillo de San Marcos translates to St. Mark’s Castle. It is located on the western shore of Matanzas Bay in the city of St. Augustine, Florida.

The first coquina stones were laid in 1672 and the building was completed in 1695. The fort would undergo many alterations and renovations over the centuries.

Forts around the coastline were important to avoid pirate attacks and masonry fortification was meant to protect the city.

Here are 10 facts about the Castillo De San Marcos.

1. Built to Protect Treasure Ships

The Castillo de San Marcos is the oldest masonry fort in the continental United States. Photo By Pom’

The fort was built to protect against the looting of the treasure from Spanish ships. It was a way of providing a homeport for their ships and troops.

For over 200 years, Fleets of the slow-moving ships laden with gold, silver, and precious stones, would move out of the Caribbean in convoys destined for Spain.

These fleets moved tons of gold, silver, and anything else of value. Pirates knew this and would lay in wait and attack the treasure fleets.

Recognizing the strategic significance of Florida for the defense of their treasure fleets, the Spanish began to settle there and thus the need for a fort.

In today’s dollar value, it’s estimated that the Spanish took well over 500 billion dollars of treasure from the new world back to Spain.

2. Over 350 Years Later, Only Two Names

While the Castillo is nearly 350 years old, it’s been known by only two different names. The Spanish named the fort after Mark the evangelist in the new testament.

When the British took over Florida in 1763 they chose to anglicize the name to Fort Saint Mark. They had Florida for only 20 years when it reverted to Spain.

Fast forward to 1821, Upon receiving the fort from Spain, the Americans changed its name to Fort Marion. It was named to honor General Francis Marion, an American Revolutionary War hero nicknamed “The Swamp Fox.” 

On 5^th June 1942, the Castillo had its original name restored by an act of congress. By then it had been a national monument for 12 years.

3. The Dry Moat

A moat is a shallow depression between the walls of a fort and its outer defenses. Its purpose is to provide an open area that allows the defenders to see any attackers that make it past the outer defenses.

While people expect moats to be filled with water, there are quite a few castles and forts that have dry moats. These moats could be easily flooded with seawater by opening floodgates on the sea wall.

Castillo’s moat is roughly 40 feet (12 meters) wide and looks better when filled with water. They preferred it dry because they were using it to graze cattle, goats, and sheep and also to store food for its residents during war times.

4. Soft Walls Made of Coquina

A picture of a cannon on Castillo de San Marcos Photo By fatzcatz –

The Castillo was made from the only local stone available in the area known as coquina. It consists of ancient shells that have bonded together to form a sedimentary rock similar to limestone.

Coquina has several desirable qualities. The stone is quite soft and so it is easy to transport and also easy for masons to cut and shape.

This type of stone was very good for building forts during the period of large cannon use. With coquina’s softness, cannonballs would sink into, like nails in wood, rather than shatter or puncture the walls.

5. The Fort’s Shape and Form

The symmetrical-shaped Castillo had walls built low enough to minimize its profile as a target for attacks but high enough to stop aggressors from surmounting the walls.

The walls were strong enough that they could support up to 16 heavy cannons and were thick enough that cannonballs would not be able to penetrate the interiors of the castle.

6. Never been Defeated in Battle

One of the four corners, The San Pablo Bastion, at night. Photo By Juliancolton –

The Castillo has been occupied by the Spanish, British, and the US but never has it ever been conquered in all the years of its operation.

Many believe its soft and porous stone walls are the reason it has survived this long.

7. Peaceful Handover

Castillo has changed hands twice without any violence or shots being fired.

The first time was after Florida withdrew from the union on 10^th January 1861 and the U.S forces left Castillo leaving only one soldier as the caretaker. When Confederate forces came he asked for a signed receipt of the property and he quietly left.

The second time was in March 1862 when confederate forces in the fort abandoned it a night before the city was surrendered to the Navy commander.

8. It has One Entrance

The Castillo de San Marcos entrance. Photo By RuggyBearLA –

The Castillo has only one entrance that faces the city. The entrance has both a drawbridge and a ravelin (the triangular detached outer structure) for good security.

Many castles and forts would also have another entrance that allowed the occupants to come and go discreetly but not the Castillo.

9. Castillo was Built by Slaves

The fort was built with the labour of indigenous slaves. While slavery was forbidden in Spanish colonies, a system called encomiendo was developed.

Encomiendo was a system that provided Spanish leaders with the labour of groups of conquered non-Christians.

The laborers, in theory, were provided with benefits by the conquerors such as food and shelter along with access to the catholic religion.

So technically the indigenous people who were held were not slaves, but their labour was mandatory and coerced. They could be killed if they tried to escape and many of them were worked to death.

10. The Four Corners and a New Roof

Aerial view of the Castillo de San Marcos. Photo By National Park Service –

The fort has four bastions named after Catholic saints. The four corners are San Pedro, San Agustín, San Carlos, and San Pablo.

Initially, the Castillo was built with wooden beams. After a few decades, the wood had rotted to a point where the structure wasn’t safe for daily use let alone during war times.

The wood was replaced by 28 stone arches and a stone deck that forms the roof. Built much later than the rest of the structure in the 1730s, the deck at its weakest point is nearly three feet or one meter thick.