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Castillo San Cristóbal’s Impressive Strategic Military Design

A Successful Plan that Prevented Invasion onto the Fort
Publication of Discovery: July 31, 2019
Issue: July, 2019

Castillo San Cristóbal (San Cristóbal Fort), located in the island of Puerto Rico, is part of the fortification system which construction began around 500 years ago under the Spanish Crown in the walled city currently known as Old San Juan. This fortress was strategically designed in order to defend Puerto Rico from enemy land invasion from the eastern side of San Juan islet. Castillo San Cristóbal is an example of great Spanish military engineering in América during the colonial era, considering the design and location of elements such as defense structures, tunnels that served as mining galleries, dry moats and sentry boxes (garitas in Spanish).

Even though I have served as a private tour guide in Castillo San Cristóbal during many years, every time I visit this place I am amazed by the strategy behind the fort’s design. Below I share my experience in regards to what most impresses me about Castillo San Cristóbal’s military design.

While walking in the tunnel that connects the castle’s square and the outer defense area, various curved tunnel walls are seen. The tunnel walls were strategically designed to complicate enemy’s efforts to fire musket guns in the tunnel without being seen by defense soldiers. Also, small niches were constructed on some tunnel walls so that defense soldiers could hide there. In addition, the tunnel ceiling has some grooves between tunnel segments. In the event enemy soldiers arrived to the tunnel, the grooves served as another defense mechanism since these could be filled with gunpowder pouches and be burned in order to explode the corresponding tunnel segments.

A communication tunnel can be seen at some point on the explored tunnel’s ceiling. This particular tunnel allowed defense soldiers to warn the battery located at the castle’s main firing area about enemy attacks in proximity to the castle’s main building. I imagine a soldier shouting: “The enemy is climbing the trenches, be prepared to explode the tunnel!”

After exiting the mining gallery tunnel, some of the outer defenses built to protect the castle’s main structure can still be admired. For instance, I walked on a dry moat that is currently located on grass near a bunker built afterwards by the United States government during World War II era. Hidden dry moats separated and protected multiple defense structures that composed the fortress.

The design and location of dry moats and diverse exterior defense structures contributed for a brilliant defense strategy: create an optical illusion that Castillo San Cristóbal comprised one structure. Even though not all outer defenses are currently present at Castillo San Cristóbal’s premises, one may see constructions such as Revellín de San Carlos (San Carlos Ravelin), a triangular fortification connected to the castle’s main building, and El Abanico, which is closer to the ocean but farther away from the main fortification. Outer defenses also had mining gallery tunnels. If enemy soldiers invaded any of these exterior fortifications, defense soldiers could explode these.

The sentry boxes also played a major role in Castillo San Cristóbal’s defense strategy. These served as observation points on the castle’s main building, various exterior defense structures and fortress walls surrounding the castle’s premises.

Every time I visit Castillo San Cristóbal, I imagine the enemy soldiers’ panoramic view from their ships as well as their invasion efforts after disembarking at El Escambrón Beach. Thanks to the ingenious strategic design of Castillo San Cristóbal and its surroundings, the enemies who dared to try to invade were not able to raise another country’s flag in the castle’s main structure during the Spanish colonization of Puerto Rico.

Following my studies about the narrated history behind Castillo San Cristóbal, I comprehend and value more this gem that was constructed to defend what today is my dear island of Puerto Rico. Currently, this fortress is my favorite touristic attraction in the island.

Now it is your turn to explore Castillo San Cristóbal, part of the San Juan National Historic Site, and witness the great military defense it represented. The San Juan National Historic Site has been designated by UNESCO as a World Heritage site.

Castillo San Cristóbal is open from Monday to Sunday, 9:00 am - 6:00 pm. Guided tours at this attraction are available on Saturdays and Sundays. For details, you may contact the San Juan National Historic Site. T. 787-729-6777

Note: During around eight years, the author, Melba Ayala, guided travelers and locals in the San Juan National Historic Site. By then, she was authorized to serve as a private tour guide by the U.S. National Park Service.

Translated by N. Michelle Rodríguez Amadeo

tour provider: Yourself onto Culture
book here
where the crew ate: At Home
photograph by: N. Michelle Rodríguez

Note: This story was accurate when it was published. Please be sure to confirm all details with the pertinent businesses before planning your trip. Please be cautious. The company behind this publication assumes no responsibility for your safety when participating in the activities mentioned in this article. You are responsible for confirming whether you are capable of participating in any of these activities or tours, regardless of the effort level or any other information provided in this website.


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Melba Ayala (San Juan, P.R.):”Every time I visit Castillo San Cristóbal, its design fascinates me.”


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