Castillo! Is it a castle or a fort? Both. As a follow-up post about Castillo de San Marcos in downtown St. Augustine, Florida, I want to reiterate that it is the oldest masonry fort in the United States with unique North American architecture. It remains as the only surviving 17th century military construction in the country.

Does it look like a castle? Well … maybe. I think it looks more like a fort though. Opening in 1695, Castillo became a showpiece for military defense engineering.

A monument not only of stone and mortar but of human determination and endurance, the Castillo de San Marcos symbolizes the clash between cultures which ultimately resulted in the unique, unified United States. Still resonant with the struggles of an earlier time, these original walls provide tangible evidence of America’s grim but remarkable history.
https://www.nps.gov/casa/learn/historyculture/construction.htm

Thank you Italy for providing the star shape design from the 15th century. I’m amazed how the architecture fit the technology of the day. Of the major architectural variations, the “bastion system,” named for the projecting diamond or angle shaped formations added onto the fort walls, was the most commonly and effectively used to combat the new weapons – cannons.

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The Spanish occupying Florida knew about the coquina rock formations along the coastline, but they were soldiers, not stonemasons or builders. Wood structures would not last against the increasing firepower and technology of invading forces.

The British, settling to the north, edged into the Carolinas. Spanish Florida was only a short sail away. How could the Spanish keep the British from taking over Florida? Apparently, the goal of the British was to set up a base of operations to attack the Spanish treasure fleets and the more wealthy colonies of the Spanish Caribbean.

To help counter this threat, the Spanish began construction on the Castillo de San Marcos in 1672 – using coquina.

Coquina Rock to the Rescue

Coquina stone was quarried in the area of present-day Anastasia State Park on Anastasia Island (part of St. Augustine). Military engineers and stonemasons were brought from Spain. Convicts and additional soldiers were brought from Cuba. Oyster shells were burned into lime and mixed with sand and water to make mortar.

Coquina rock is a type of sedimentary rock such as limestone. It was formed by the deposits and cementing together of mineral and organic particles on the ocean floor or other bodies of water on the surface.

The coquina rock used at Castillo de San Marcos was likely retrieved from the formation that stretches from St. Augustine to Palm Beach County, Florida.

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According to geologists, thousands of years ago, the tiny coquina clam donax variabilis lived in the shallow waters of coastal Florida, as they still do today. These are the small pink, lavender, yellow, or white shells one sees along the beach at the waterline.

As the resident clam died, the shells accumulated in layers, year after year, century after century, for thousands of years, forming submerged deposits several feet thick. During the last ice age, sea levels dropped, exposing these shell layers to air and rain. Eventually, the shell became covered with soil, then trees and other vegetation. Rain water percolating through the dead vegetation and soil picked up carbon dioxide and became carbonic acid, the same ingredient that makes soda fizz. (National Park Service)

By the way, one of the best coquina rock formations is at Washington Oaks, between Crescent Beach and Marineland, Florida, on the Atlantic Ocean. It’s worth a trip to enjoy the beach and see the rock formations. https://www.floridastateparks.org/learn/geology-coquina-rocks

As the weak acid soaked downward, it dissolved some of the calcium in the shells, producing calcium carbonate, which solidified in lower layers, much like how flowstone and stalactites are formed in caves. This material “glued” the shell fragments together into a porous type of limestone we now call coquina, which is Spanish for “tiny shell”.

Given its light and porous nature, coquina would seem to be a poor choice of building material for a fort. However the Spanish had few options. Coquina was the only stone available on the northeast coast of La Florida. The porous coquina actually became an unexpected benefit – with its mixture that contained millions of microscopic air pockets that allowed it to compress.

The walls being constructed for the Castillo would be untested but the coquina was the only way to give the Spanish a fighting chance against the British. The inner courtyard was designed for the town residents to take refuge when under attack.

It’s a good thing the Spanish acted quickly to build a stronger structure. In 1702, Governor James Moore of Charleston led his English forces against St. Augustine and the Castillo. He captured the town and set his cannon up among the houses to bombard the fortress.

What happened? Strangely, instead of shattering, the coquina stone merely compressed and absorbed the shock of the hit. The cannon balls just bounced off or sunk in a few inches. The shell rock worked! I think the bastion, angled system contributed quite a bit too.

A cannon ball fired at more solid material, such as granite or brick, would shatter the wall into flying shards; but cannon balls fired at the walls of the Castillo burrowed their way into the rock and stuck there, much like a bb would if fired into Styrofoam. So the thick coquina walls absorbed, or deflected projectiles rather than yielding to them, providing a surprisingly long-lived fortress (or is it a castle)?

Even when General Oglethorpe attacked St. Augustine in 1740 and bombarded the Castillo for 27 days, the walls held firm. The rock made of seashells turned out to be an excellent building material. When the Spanish decided to fortify the southern approaches to St. Augustine by building Fort Matanzas later that year, they again used coquina stone, and, like the Castillo, this smaller fort was never captured.

What if the Spanish did not have this stone? If not for coquina, perhaps the British would have captured St. Augustine much earlier than 1763, when they finally gained Florida by treaty. If the British gained Florida earlier, it’s possible the course of the American Revolution would have changed. Maybe the U.S. would still be a part of Great Britain. The history of the U.S.A. could have been much different had it not been for little clams, and coquina.

Fort or Castle?

Again, is the Castillo a fort or castle? I guess there isn’t a clear answer. According to Wikipedia,  a castle is a private, fortified residence. Merriam-Webster dictionary says a castle is “a large fortified building or set of buildings; a retreat safe against intrusion or invasion.”  Oxford English Dictionary says it is “a large building, typically of the medieval period, fortified against attack with thick walls, battlements, towers, and in many cases a moat.”

The Castillo de San Marcos fits all of those definitions in one way, or at one time or another. When it was first built, the governor of St. Augustine resided inside the building, which would make it a “private fortified residence.” It is most definitely a large, fortified building that provided a retreat safe for the people of St. Augustine against invasion. At one time it housed about 1,500 people for 51 days while the English laid siege. It also has thick walls, battlements, towers and a moat. 

Most of the fortifications the Spanish built in the new world were named Castillos. Perhaps it is a hold-over from medieval times, meant to inspire their people and instill fear in their enemies? The Spanish were fond of decoration and embellishment in the physical designs of their fortresses; they may have felt the same about their names. As of yet, there has been no documentation found explaining exactly why they chose to use Castillo rather than Fuerte or Fortaleza. However, it is interesting to note that the wooden fort preceding the current stone one was also called Castillo de San Marcos. 

Also interesting is the fact that it does later become referred to as a fort. When the British gained Florida through the 1763 Treaty of Paris, they renamed the building Fort Saint Mark. The United States Army decided in 1825 to call it Fort Marion. Under those occupations, it was indeed used solely for military functions.

The British and the Americans did not plan to use it as a place of refuge for the citizens of St. Augustine. They both used the fort as barracks, for military storage, and a few times as a military prison. The National Park Service and United States Congress decided to restore its original name in 1942, in honor of its unique Spanish history, so it went back to Castillo de San Marcos for good.  I say it’s a fort.

Blessings along the Way!

Ron