Hornwork of Castillo San Felipe del Morro, San Juan National Historic Site
Castillo San Felipe del Morro Main Page
As you walk across the esplanade (large field) from Norzagaray Street towards Castillo San Felipe del Morro (aka El Morro) at San Juan National Historic Site, what you are looking at are two bastions and a curtain (the technical name for the wall between two bastions). The Spanish named the bastion on the left Austria and the one on the right Ochoa. Along with the curtain, these features make up what is known as a hornwork because its shape is like the head of a bull—two horns on the side and a forehead in the middle. A third bastion that is adjacent to Ochoa, Carmen, was added in the 1770s, taking the place of an existing artillery battery.
Bastions are structures that protrude out from the fort walls. If a fort were square or rectangular and the enemy reached the walls, the only thing the soldiers in the fort could do would be to hang over the walls and shoot down at them or to drop rocks on their heads. Cannon would be useless. With bastions, every wall in the fort can be covered by rifle or artillery fire of some sort.
El Morro, which is triangular in shape, has bastions at all three points (Santa Barbara Bastion faces the ocean), and these bastions themselves have angular walls, which means even the walls of the bastions are covered. The following graphics illustrate how bastions work. On the satellite image of El Morro, the white lines represent the many possible lines of fire.
Example of coverage possible by men stationed in a bastion
Example of coverage possible by men stationed in the bastions of El Morro
The bastions of many forts have interior rooms at ground level that house artillery so that when the enemy enters the moat, they would be caught in a crossfire. The cannon typically shoot nails or cannister (small metal balls like a shotgun). Many fort walls also have rifle ports that soldiers can shoot out from. El Morro has none of these features because the interiors of the bastions have no rooms. The walls are just retaining walls, and the interiors are filled with dirt and rubble. Enemies who make it to the walls would only be subject to musket and artillery fire from above.
Wall of Castillo San Felipe del Morro’s Austria Bastion, San Juan National Historic Site
Bastion walls of the Advanced Redoubt at Fort Barrancas in Florida
El Morro was built to protect the entrance into San Juan Bay, and most of its guns were pointed seaward. Less concern was given to protecting the fort from a land invasion, and thus its rear was quite vulnerable. There were bastions at the rear, but they were not very well built. In fact, the fort was captured by the British in 1598. Luckily for the Spanish, an outbreak of dysentery two months later forced the English to abandon Puerto Rico, leaving them in control once again.
The British success at San Juan prompted the Spanish to enhance the landward side of the fort, and in 1602 the original hornwork was rebuilt. This construction resulted in the first iterations of the Ochoa and Austria bastions and the curtain. In addition, a retaining wall was built between Ochoa and a small structure called the Mercado Demi-bastion (half bastion), which was constructed around the same time. Mercado still exists today, but it is closed to the public due to the deterioration of the staircase that leads down to it. The embrasure on top (gap in the wall that cannon fired out from) is the only remaining embrasure at El Morro from the 17th century.
Mercado Demi-Bastion
A plaque on both the Ochoa and Austria bastions is inscribed with the date 1606, which may be when they were completed. However, there are documents that suggest construction continued slowly for fifteen more years due to budget constraints. Perhaps the plaques were attached prematurely? A written diagram from 1625 shows the hornwork, so the features were definitely completed by then. The Dutch attacked San Juan that same year and failed to take the fort, so the improvements seemed to have worked. The Dutch did, however, burn the entire town outside the fort before they left San Juan. This sparked the construction of both a wall around the city and Castillo San Cristóbal. Both projects were started in 1634.
The general condition of all fortifications in San Juan by the early 1700s was poor. Construction was shoddy to begin with, and the weather and sea elements had taken a toll on the forts. In 1765, the Spanish sent Irishman Alexander O’Reilly to San Juan to come up with a proposal to overhaul the fortifications, particularly El Morro and San Cristóbal. O’Reilly had earlier made recommendations to improve the fortifications in Cuba. Work began in 1766 and lasted until the end of the 1780s.
In 1773, the hornwork of El Morro was torn down to about two feet below a new proposed level for the moat floor (the plan was to raise the moat floor nine feet). This foundation was used as a base to rebuild the walls of the bastions and curtain. In doing so, the terrepleins (artillery decks) were raised roughly eleven feet. With the moat floor being raised as well, the overall height from ground to terreplein remained relatively the same. (Note that the 1606 plaques were removed from the original bastions and reattached to the new ones.)
There was talk of building a ravelin to protect the sally port (entrance), and perhaps the increased elevation was required for the cannon on the bastions to be able to shoot over the top of the ravelin, which ultimately was never built. A ravelin is a small fortification, typically triangular or semicircular in shape, that blocks direct access to the fort’s sally port. Attacking forces would have to make it around the ravelin before beginning an assault on the actual fort. Castillo San Cristóbal has a ravelin, the San Carlos Ravelin.
The wall opposite the curtain of Castillo San Felipe del Morro, which is named the Great Wall, started out as nothing more than a much shorter retaining wall. During the 1770s construction, its height was raised as well. When casemates (fortified rooms for artillery) were installed on both sides of the Plaza de Armas (main plaza), the roofs were used to create wide terrepleins for both the curtain and the Great Wall. The entire structure, which forms a loop around the plaza, is now known as the Cavalier Battery. Cavalier is the term used for the highest structure of a fort.
Great Wall and Cavalier Battery of Castille San Felipe del Morro
Upon entering Castillo San Felipe del Morro, you will be on the Plaza de Armas. At either end is an archway. If facing the fort entrance, the archway on the right leads to the Austria Bastion and the one on the left to the Carmen Bastion, and from there you can get to Ochoa. Once at the top, you can walk around the entire Cavalier Battery.
See the following web pages for photos and more information about the hornwork structures and the Cavalier Battery.
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Last updated on April 8, 2024
